v1.12 track B.3: agent whitelists + .codecontextignore template + CLAUDE.md updates

Removed /opt/boocode/AGENTS.md (per-project override) — the project's
agents now resolve from the global /data/AGENTS.md only. Eliminates the
two-files-must-stay-in-sync footgun that surfaced during B.3
verification.

Fix: agents.ts ALL_TOOL_NAMES was a hardcoded 9-item whitelist that
silently filtered any unknown tool name from agent.tools arrays. This
caused web_search/web_fetch (v1.11.8) and the 8 codecontext tools to be
dropped at parse time. Replaced with ALL_TOOLS.map(t => t.name) for
single source of truth. Pre-existing exposure was dormant since no
builtin agent listed web_search; surfaced by adding codecontext.

codecontext/.codecontextignore.template

@@ -0,0 +1,33 @@
+# .codecontextignore — paths codecontext skips during analysis
+# Copy to your project root and customize. Same syntax as .gitignore.
+
+# Dependencies / vendored code
+node_modules/
+vendor/
+.venv/
+venv/
+__pycache__/
+target/
+
+# Build artifacts
+dist/
+build/
+out/
+.next/
+.nuxt/
+.svelte-kit/
+
+# IDE / tooling
+.opencode/
+.vscode/
+.idea/
+
+# Test artifacts / coverage
+coverage/
+.nyc_output/
+.pytest_cache/
+
+# Lock files (rarely have meaningful symbols)
+package-lock.json
+yarn.lock
+pnpm-lock.yaml