fix(coderabbit): resolve all 12 findings on PR #3152

MAJOR (security/correctness):
- commands/gsd/debug.md: add Write to allowed-tools (session file creation
  requires it — workflow explicitly says 'use Write tool, never heredoc')
- workflows/debug.md: add SLUG sanitization guard to steps 1b+1c (status/
  continue subcommands used raw user input in file paths — path traversal)
- workflows/thread.md: sanitize $ARGUMENTS in RESUME mode before file path
  construction (was bypassing the sanitization guard in CLOSE/STATUS modes)

MINOR (consistency/correctness):
- docs/INVENTORY-MANIFEST.json: remove stale top-level 'workflows' array
  (duplicate of families.workflows introduced in earlier update)
- commands/gsd/resume-work.md: normalize process to 'Execute end-to-end.'
- commands/gsd/settings.md: normalize process to 'Execute end-to-end.'
- commands/gsd/update.md: normalize otherwise branch to 'execute end-to-end.'
- docs/adr/0002: add Status: Accepted + Date header (ADR convention)
- workflows/extract-learnings.md: rename step extract_learnings → extract-learnings
- tests/extract-learnings.test.cjs: tighten step-name assertion to exact name

ARCHITECTURE:
- scripts/command-contract-helpers.cjs: extract CANONICAL_TOOLS, parseFrontmatter,
  executionContextRefs as shared module — single source of truth consumed by
  both lint script and test suite (prevents silent lint/test disagreement)
- scripts/lint-command-contract.cjs: require() helpers instead of duplicating
- tests/command-contract.test.cjs: require() helpers; move readFileSync calls
  inside test() callbacks (registration-time throws surface as named failures)

docs/adr/0002-command-contract-validation-module.md

@@ -1,5 +1,8 @@
 # Command Contract Validation Module
 
+- **Status:** Accepted
+- **Date:** 2026-05-05
+
 We decided to centralize the `commands/gsd/*.md` file contract into a single validation seam enforced at two layers: a fast lint script (`scripts/lint-command-contract.cjs`) that runs as a pre-test CI step, and a behavioral regression test (`tests/command-contract.test.cjs`) that validates the full contract against the live filesystem.
 
 ## Decision