ci(pr): drop redundant ruff/format/mypy from the heavy backend job

[SoundMindsAI]

What

Removes the redundant ruff check / ruff format --check / mypy backend/ steps from the heavy backend job in .github/workflows/pr.yml. All three are already covered by the always-run static-checks-backend job (no service containers, sub-minute feedback), so re-running them in the heavy lane only burned ~30-40s of critical path.

Also:

• Removes the now-unused Restore mypy + ruff caches step (it only served the removed ruff/mypy steps).
• Renames the job display name backend (lint + typecheck + tests + coverage) → backend (tests + coverage) for accuracy.

Why

The heavy backend job is the per-PR critical-path bottleneck (~9 min). This is the reliable, zero-risk slice of chore_pr_yml_parallelize_backend_job: a lint failure still goes red via static-checks-backend; this lane just no longer self-aborts early on a lint failure (acceptable — GHA doesn't auto-cancel, and the PR is already red).

Scope decision

This is the lint-dedup only. The lane-split (parallel unit+contract + serial integration + coverage combine) and split-integration-by-service-container were deferred to a new idea: docs/00_overview/planned_features/02_mvp2/infra_pr_yml_split_backend_test_lanes/idea.md. Rationale: the integration layer is the binding constraint and can't run under -n auto (FK-teardown collision, reverted on PR #291), so the lane-split's residual win is only ~1-1.5 min and needs a blind-CI-validated coverage-combine path — not worth bundling here.

Docs

• docs/06_vendor_docs/github-branch-protection.md: adds the static-checks-* jobs to the required-checks set (lint/type now lives there, not in the heavy backend job) and updates the renamed check name. Keeps the canonical branch-protection setup guide accurate for when protection is configured (not active today).
• Reframes chore_pr_yml_parallelize_backend_job/idea.md to the shipped lint-dedup; obsolete full-pipeline feature_spec.md + pipeline_status.md (from the abandoned spec→plan path) removed.

Risk

No Python/frontend source touched — workflow YAML + Markdown only. YAML validated (yaml.safe_load). No test parses the job display name or validates these doc links.

https://claude.ai/code/session_016aMKimAFu2wouGCtWNdCLz

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Generated by Claude Code

[gemini-code-assist]

Code Review

This pull request updates the documentation to reflect the descoping of the backend CI parallelization chore. It modifies the existing chore idea to focus solely on removing redundant linting and typechecking steps, introduces a new idea document for the deferred parallel test lanes, and updates the GitHub branch protection guidelines to include the separate static check jobs. The review feedback correctly identifies broken relative links in the updated idea document that need to be adjusted to the correct directory depth.

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[SoundMindsAI]

Gemini review adjudication

#	Severity	Finding	Verdict
1	Medium	Repo-root relative links in the idea's PREFLIGHT REFRESH block were one ../ short (file is 5 levels deep, links used 4)	Accept — fixed in ec013dc (verified both targets now resolve to real files via os.path.normpath)

One finding, accepted and fixed. No other findings.

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Generated by Claude Code