docs: sync #112 complexity budget and tracing CI lane

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Summary

Documentation-only sync after #112 (and the already-merged #102/#104 docs) so operator docs match current main.

Docs added/updated

• README.md — architecture, quality gate, Laminar section, troubleshooting
• AGENTS.md — toolchain, suite counts, complexity ownership
• SPEC.md (S20 / S22), EVALUATION.md (S20 / S22), BUILDPLAN.md (T21 / T23)
• docs/superpowers/specs/2026-07-15-tech-debt-cicd-routine-design.md — two CI jobs

Codepaths covered

• complexity_gate.DEFAULT_THRESHOLD / --isolated C901 measurement (Fix two checks that appeared to run and didn't: inert complexity budget, CI-skipped real-SDK tracing test #112)
• .github/workflows/ci.yml gate + tracing jobs (Fix two checks that appeared to run and didn't: inert complexity budget, CI-skipped real-SDK tracing test #112)
• cli.py / observability/ / tracing.py opt-in contract (Make CLI tracing explicitly opt in #104; already documented, CI lane added)
• pyproject.toml — no logfire in dev, no inert mccabe budget

Knowledge gaps addressed

• Docs still cited [tool.ruff.lint.mccabe] max-complexity as the budget after Fix two checks that appeared to run and didn't: inert complexity budget, CI-skipped real-SDK tracing test #112 removed it
• S20 / dev group still mentioned logfire after Make CLI tracing explicitly opt in #104 removed it
• CI tracing job undocumented (real-SDK tests could appear to "pass" via skip on gate alone)
• Suite counts refreshed: 748/4 default install; 749/3 with --extra tracing

Notes

• Prefer closing older open docs drafts (docs: ensure_deps SHA pin, Laminar opt-in, Harbor WIDS D2, suite 746 #109/docs: ensure_deps SHA pin, Laminar opt-in, Harbor WIDS D2, suite 746 #110/docs: ensure_deps SHA pin, Laminar opt-in, Harbor WIDS D2, suite 746 #111/docs: sync ensure_deps/Laminar/Harbor gaps and #112 complexity + tracing CI #113/docs: sync ensure_deps/Laminar/Harbor gaps and #112 complexity + tracing CI #114/docs: sync ensure_deps/Laminar/Harbor gaps and #112 complexity + tracing CI #115) as superseded once this lands
• No runtime / test code changes

Verification

• Re-read complexity_gate.py, pyproject.toml, .github/workflows/ci.yml, tests/test_complexity_gate.py, tests/test_observability.py
• uv run pytest -q → 748 passed / 4 skipped
• uv sync --extra tracing && uv run pytest -q → 749 passed / 3 skipped