chore(ci): add backend Ruff and Mypy checks

[hardikuppal04]

Summary

The backend had no enforced Python lint, formatting, or type-analysis gate in CI. That left roughly 32,000 lines of application Python without a static quality baseline. This PR establishes a mergeable, pinned baseline without changing runtime behaviour.

Linked issue

Closes #188

Roadmap alignment

• Roadmap §23 workstream this advances: backend engineering-quality and reliability gates.
• §28 market-fit criterion this moves toward: repeatable, trustworthy code-quality analysis. The referenced roadmap HTML is not present in this checkout, so this PR does not claim an unverifiable exact criterion number.
• Accepted evidence it is real (test/usage/repo state, not intent): CI executes ruff check app, ruff format --check app, and mypy app before backend tests; all three commands pass locally against this branch.

What changed

• Added pinned, dev-only ruff and mypy tooling to apps/backend/pyproject.toml and the backend development requirements.
• Added Ruff’s 120-column Python-3.12 configuration, correctness lint rules, and one documented compatibility re-export exception.
• Added a passing Mypy baseline with explicit, module-scoped existing-type-debt entries. The unchecked modules are listed rather than globally disabling Mypy, allowing the baseline to be ratcheted down incrementally.
• Added Ruff lint, formatter, and Mypy commands to the backend CI job before the existing test step.
• Documented the exact local static-analysis setup and commands in apps/backend/README.md.
• Applied the maintainer-authorized formatting baseline. The 43 changed application Python files are AST-equivalent to upstream/dev; the cosmetic changes are isolated from the tooling/configuration commit.

Acceptance criteria completed

• Ruff and Mypy run in the backend CI job.
• The baseline is pinned and mergeable: Ruff reports no selected correctness findings, all 117 application files are formatted, and Mypy passes with named per-module debt entries instead of a global ignore.
• Local setup and commands are documented in apps/backend/README.md.
• Tooling is dev-only: the optional dev dependency group and development requirements changed; runtime dependencies, Dockerfiles, and production install paths did not.

Testing performed

# apps/backend
.\.venv\Scripts\ruff.exe check app
# PASS: All checks passed!

.\.venv\Scripts\ruff.exe format --check app
# PASS: 117 files already formatted

.\.venv\Scripts\mypy.exe app --no-incremental
# PASS: Success: no issues found in 117 source files

.\.venv\Scripts\python.exe -m pip check
# PASS: No broken requirements found.

.\.venv\Scripts\python.exe -m pytest -q --junitxml <temporary-report> --basetemp <temporary-directory>
# PASS: 709 passed, 5 skipped, 930 warnings in 194.23s
# JUnit: 714 tests, 0 failures, 0 errors, 5 skipped

# repository root
npm.cmd run lint:frontend
# PASS

npm.cmd run build:frontend
# PASS: TypeScript build and Vite production build completed

# apps/frontend
npm.cmd exec -- vitest run src/app/routes/accessibility.test.tsx src/app/routes/router.test.tsx --coverage --reporter=json --outputFile=<temporary-report>
# PASS: 13 passed, 0 failed (the command's subset coverage thresholds then exit non-zero, as expected for a subset run)

# full frontend suite
npm.cmd --prefix apps/frontend run test
# NOT GREEN LOCALLY: 197 passed, 2 failed. The failures are the existing Dashboard assertions in
# accessibility.test.tsx and router.test.tsx, which pass in the targeted run above. This PR changes no
# frontend source or test configuration; the result appears order-dependent on the rebased base and is
# reported here rather than hidden.

npm.cmd run docker:config
npm.cmd run docker:validate
# NOT RUNNABLE LOCALLY: both require Docker, which is not installed on this host.

Screenshots

Not applicable — there is no UI change.

Security and data considerations

No runtime request, authentication, authorization, data, migration, or logging behaviour changes. Ruff and Mypy are pinned development tools only; no secrets, environment files, or generated artifacts are included. Static analysis reduces detection latency but does not itself prove the absence of all defects.

Dependencies and blocked work

None. Docker-specific validation is unavailable on this host because the Docker executable is not installed; CI remains responsible for that environment.

Scope changes or remaining work

The maintainer explicitly authorized a one-time 43-file formatting baseline in the same PR. Because dev advanced during implementation, three additional files that would fail the new formatter check were reformatted in separate cosmetic commits. All 43 formatted files were checked for AST equivalence.

The Mypy baseline deliberately records existing debt as explicit per-module configuration. Tightening or removing those entries is follow-up ratchet work, not a claim of full type coverage.

Contributor checklist

• This PR targets dev
• I claimed the issue and had it assigned or acknowledged before starting substantial work
• The branch was created from an up-to-date upstream/dev
• The branch is rebased on the latest upstream/dev
• This PR addresses one clearly scoped issue
• This PR advances a §23 workstream toward a §28 market-fit criterion (Roadmap alignment filled)
• Every acceptance criterion I claim as complete is actually complete
• Relevant backend tests pass; the unrelated full-frontend result is disclosed above
• Documentation is updated for the new local developer workflow
• No secrets, credentials, local env files, or generated artifacts are included
• No unrelated files were changed; the formatting baseline is maintainer-authorized issue scope
• Closing syntax (Closes) is used only because the issue is fully resolved
• Dependencies and follow-up work are linked

[parthrohit22]

Approving — no correctness issues found, and the formatting claim holds up under
independent verification. Notes below are follow-ups, not blockers.

Formatting claim verified, with one caveat.

I replayed ruff format from origin/dev across all 43 changed Python files using
this PR's own pinned config. 42 are byte-identical to the branch. The 43rd,
app/analysis/architecture.py, differs in two places where the branch adds magic
trailing commas that force expansion:

ArchLayer(id=layer, name=..., order=..., nodes=node_ids)   # dev, ruff-stable
ArchLayer(                                                  # branch, also ruff-stable
    id=layer, ..., nodes=node_ids,
)

Both variants pass ruff format --check and are semantically identical, so nothing
is broken and CI is correct either way. Flagging only because the PR body describes
the 43 files as formatter output, and two hunks there are hand edits.

(AST comparison wasn't usable as a cross-check — the repo uses PEP 695 generics in
query_service.py — so the format replay is the stronger evidence regardless.)

The Mypy baseline is thinner than the PR body reads.

The 29 ignore_errors = true modules cover every route module, every service, the
worker, query_service, resolution, extraction/python, and
extraction/typescript — effectively all the interesting logic. What stays checked
is largely schemas and models. The per-module, explicitly-named approach is exactly
the right shape and much better than a global disable, but
"Success: no issues found in 117 source files" reads considerably stronger than the
actual coverage. Please open a follow-up issue tracking the ratchet-down so the
override list doesn't calcify.

Scope gap worth documenting.

ruff check app / mypy app leave tests/ and scripts/ unchecked. Reasonable
for a first baseline — please state it in apps/backend/README.md as the intended
scope so nobody assumes coverage that isn't there.

Rule set note. ["E4","E7","E9","F"] is narrow — no I, B, UP, SIM.
Sensible for a mergeable baseline; candidates for the same ratchet issue.

Merge coordination: this conflicts with #227 in .github/workflows/ci.yml and
app/extraction/support_matrix.py, and #227's new registry code fails
ruff format --check under this config. Suggest landing this one last so the
formatter baseline absorbs #227's code in a single pass.

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