feat(provider): add Atlas Cloud preset

[binyangzhu000-sudo]

Summary

Add Atlas Cloud as a first-class OpenAI-compatible provider preset with:

• the API root used by cc-haha's managed /v1/chat/completions proxy path
• deepseek-ai/deepseek-v4-pro as the default model for every Claude model slot
• API-key authentication and existing model discovery support

No documentation, dependencies, lockfiles, or promotional metadata are changed.

Feature Quality Contract

• Changed surface: provider-runtime
• Tests added or updated:
  • preset registry contract assertions for endpoint, API format, auth strategy, and default model mapping
• Coverage evidence:
  • bun run check:coverage: 5 suites passed, 0 failed; no changed executable production lines matched the coverage scopes
• E2E / live-model evidence:
  • bun run check:provider-contract: 20 deterministic suites passed
  • credential-backed local smoke: model catalog returned 123 models and included the default; direct connectivity and the Anthropic-to-OpenAI proxy pipeline both returned HTTP 200
• Known risk / rollback:
  • provider availability remains dependent on upstream credentials and service availability; rollback is removal of the single preset entry and its assertions

Verification

• I ran the relevant local checks, or explained why they do not apply.
• I added or updated same-area tests for every production behavior change.
• I ran the checks selected by bun run check:impact; if I claim PR-ready/full validation, I also ran bun run verify.
• New or changed executable production lines meet the changed-line coverage threshold, or the blocker/maintainer override is documented.
• I attached or summarized the quality report path, JUnit/log artifact path, and pass/fail/skip counts.
• I ran deterministic E2E/contract checks for cross-boundary changes. Live-model evidence is attached when a trusted maintainer ran it, otherwise it is explicitly marked not run.

Additional check details:

• bun --no-env-file test src/server/__tests__/provider-presets.test.ts: 10 passed, 0 failed
• bun run check:provider-contract: 20 deterministic suites passed
• bun run check:coverage: 5 passed, 0 failed
• bun run check:server: 2,760 tests passed; three initial failures were caused by the clean clone missing the separately locked adapters dependencies. After installing adapters/bun.lock, both affected suites passed: 64 passed, 0 failed.
• git diff --check: passed

Risk

• This PR does not touch CLI core paths, or it has maintainer approval for allow-cli-core-change.
• Production code changes include matching tests, or have maintainer approval for allow-missing-tests.
• Coverage baseline/threshold changes have maintainer approval for allow-coverage-baseline-change.
• Any quarantine-policy change has maintainer approval; deterministic provider/chat contract tests were not quarantined.
• Provider/runtime changes are covered by offline mock/fixture contract tests; live smoke was run by a trusted maintainer or explicitly deferred.

[github-actions]

PR quality triage

Changed areas: area:server

CLI core policy: No CLI-core policy block detected.

Missing-test policy: No missing-test policy block detected.

Coverage baseline policy: No coverage-baseline policy block detected.

CLI core files:

• none

Coverage policy files:

• none

Required check plan:

• See PR Quality / scope-plan; it is the single source of truth for selected jobs.

Test coverage signals:

• No obvious missing-test signal from changed paths.

Risk notes:

• Provider/search behavior changed: PR gate uses mock tests; live-provider tests stay maintainer-only.

Hard merge gates come from the deterministic GitHub Actions contract lanes above.