chore(taskfile): trim to ≤100 lines (90), drop pure CLI wrappers

[Doctacon]

Summary

• Taskfile.yaml 163 → 90 lines (target ≤100 per ticket:taskfile-trim)
• Drops pure CLI wrappers: setup (folded into install), staging:generate, staging:check, check:layout, default
• Remaining 16 targets are all compose / env-setting / forker-facing defaults, each with a desc:
• docs/commands.md gains a Source layout + staging codegen section for the dropped wrappers
• CLAUDE.md Task block reflects the new shape

Closes ticket:taskfile-trim — final ticket of initiative:scaffold-polish.

Task list after trim

* ci:                 Every CI gate: ruff + mypy + pytest + secret scan + staging drift
* clean:              Remove build + test + cache artifacts
* clean-all:          Clean + drop .venv, data/, .dlt_state/
* full-refresh:       Every dlt source + SQLMesh + Soda via Dagster
* init:               Rebrand a fresh fork from scaffold.yaml
* install:            Bootstrap .venv, copy .env, uv sync, install pre-commit hook
* new-source:         Scaffold a new dlt source
* promote:            Auto-apply dev → prod promotion
* streamlit:          Launch Databox Explorer
* verify:             Smoke full-refresh — DATABOX_SMOKE=1
* dagster:dev:        Launch Dagster UI
* db:reset:           Delete local DuckDB files
* docs:build:         Render notebooks, generate dictionary + cost page, build MkDocs
* plan:dev:           SQLMesh plan against the dev virtual env
* plan:prod:          SQLMesh plan against prod
* verify:dev:         Run every Soda contract against __dev schemas

Test plan

• wc -l Taskfile.yaml ≤ 100 (got 90)
• task --list renders all 16 targets with descs
• task ci invokes cleanly through install → ruff → format → pytest → secret scan → staging drift (mypy pre-existing errors unchanged; continue-on-error in CI)
• README Quickstart commands still resolve (install, full-refresh, dagster:dev, plan:dev, verify:dev, plan:prod, streamlit, init, verify, ci)
• CI green on this PR

🤖 Generated with Claude Code