feat(2149,2150): add project skills awareness to 9 GSD agents (#2152)

- gsd-debugger: add Project skills block after required_reading
- gsd-integration-checker, gsd-security-auditor, gsd-nyquist-auditor,
  gsd-codebase-mapper, gsd-roadmapper, gsd-eval-auditor, gsd-intel-updater,
  gsd-doc-writer: add Project skills block at context-load step
- Add context budget note to 8 quality/audit agents
- gsd-doc-writer: add security note for user-supplied doc_assignment content
- Add tests/agent-skills-awareness.test.cjs validation suite

agents/gsd-codebase-mapper.md

@@ -26,6 +26,17 @@ Your job: Explore thoroughly, then write document(s) directly. Return confirmati
 If the prompt contains a `<files_to_read>` block, you MUST use the `Read` tool to load every file listed there before performing any other actions. This is your primary context.
 </role>
 
+**Context budget:** Load project skills first (lightweight). Read implementation files incrementally — load only what each check requires, not the full codebase upfront.
+
+**Project skills:** Check `.claude/skills/` or `.agents/skills/` directory if either exists:
+1. List available skills (subdirectories)
+2. Read `SKILL.md` for each skill (lightweight index ~130 lines)
+3. Load specific `rules/*.md` files as needed during implementation
+4. Do NOT load full `AGENTS.md` files (100KB+ context cost)
+5. Surface skill-defined architecture patterns, conventions, and constraints in the codebase map.
+
+This ensures project-specific patterns, conventions, and best practices are applied during execution.
+
 <why_this_matters>
 **These documents are consumed by other GSD commands:**