ci: docs-check — require doc updates for feat PRs that change the CLI surface

[JonasJesus42]

Keeps docs in sync with the CLI/check surface.

docs-check.yml — on a PR that changes the command/check surface (src/cli.ts, src/commands/**, src/checks/**, the .parityrc parser) without touching docs/**:

• feat PR → blocked (fail the check).
• fix PR → warning (non-blocking).
• Bypass: tick "Docs not needed" in the PR body, or add the skip-docs label. Re-runs on edit/label so the bypass takes effect immediately.

Uses the conventional-commit PR title for the feat/fix distinction; mirrors ci.yml's base-ref diff (fetch-depth: 0). Logic simulated locally across all cases (feat/fix/docs/checkbox/label/no-surface).

Also adds .github/PULL_REQUEST_TEMPLATE.md with the docs checkbox, and a skip-docs label.

• Docs updated (docs/** and the Parity section on deco-sites/docs)
• Docs not needed (CI/tooling only — no CLI/check surface change)

🤖 Generated with Claude Code

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Summary by cubic

Enforces docs updates when a PR changes the CLI/check surface. Previously unguarded; now feat PRs that change the surface without docs fail CI, and fix PRs get a warning.

• Detects surface changes in src/cli.ts, src/commands/**, src/checks/**, and the .parityrc parser at src/ignore/parser.ts.
• Requires updating docs/** (and the Parity section on deco-sites/docs) when the surface changes.
• Bypass: tick “Docs not needed” in the PR body or add the skip-docs label. The check re-runs on edit/label.
• Determines feat vs fix from the conventional-commit PR title; diffs against the base with fetch-depth: 0.
• Adds .github/PULL_REQUEST_TEMPLATE.md with a docs checkbox. CI-only; no runtime changes.

^{Written for commit 0cd901d. Summary will update on new commits.}