feat: scaffold Brain of Reese — FastAPI RAG chat over Postgres 17 + pgvector

Foundation (phase 01, verified):
- FastAPI app: /api/health, /api/suggestions, /api/chat (placeholder),
  static frontend served locally (no CDN)
- Postgres 17 + pgvector via db/Containerfile + compose.yaml
  (podman compose up -d db), Alembic initial migration (documents,
  chunks with vector(768), query_log)
- LLM client targeting https://aipi.reeseapps.com/v1 (turbo/embed);
  scripts/llm_probe.py verified models + 768-dim embeddings live
- Conditional debugpy: imported only when DEBUGPY=1 (attach on demand,
  :5678); logging config for clean single-line logs
- Frontend shell: mobile-first chat + Sources pages, tokens, a11y baselines
- Tests: 24 unit+integration (99% coverage on app/), ruff + pyright clean,
  Playwright smoke E2E (3 tests) against a deterministic mock LLM
- Planning: .agent/PLAN.md (architecture + LOCKED decisions), AGENTS.md,
  6 user stories, 7 phase files (one story / one phase / one Playwright
  suite each)

.gitignore

@@ -0,0 +1,29 @@
+# --- Python ---
+__pycache__/
+*.py[cod]
+*.egg-info/
+.venv/
+.pytest_cache/
+.ruff_cache/
+.pyright/
+.mypy_cache/
+.coverage
+coverage.xml
+htmlcov/
+
+# --- Environment / secrets ---
+.env
+.env.*
+!.env.example
+
+# --- Planning / agent pipeline state (committed on demand with `git add -f .agent/...`) ---
+.agent/
+
+# --- Frontend build artifacts (sources live in frontend/, builds are local-only) ---
+node_modules/
+frontend/dist/
+
+# --- Logs & misc ---
+*.log
+.DS_Store
+Thumbs.db