chore: improve agent readiness — AGENTS.md, dependabot, CODEOWNERS, labels

- Add AGENTS.md with build commands, project structure, conventions
- Add .github/dependabot.yml for automated pip + actions updates
- Add .github/CODEOWNERS for review routing
- Expand .gitignore (.env, .DS_Store, IDE configs, coverage, venvs)
- Add C901 complexity rule to ruff (max-complexity=25, benchmarks excluded)
- Add --durations=10 to pytest CI for test performance tracking
- Add docs/schema.sql for knowledge graph schema documentation
- Created P0-P3 priority + area/* + security/performance/docs labels

.gitignore

@@ -6,3 +6,30 @@ __pycache__/
 .pytest_cache/
 mempal.yaml
 .a5c/
+
+# Environment
+.env
+.env.*
+
+# OS
+.DS_Store
+Thumbs.db
+
+# IDEs
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# Coverage
+htmlcov/
+.coverage
+coverage.xml
+
+# Virtual environments
+.venv/
+venv/
+
+# ChromaDB local data
+*.sqlite3-journal