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)

AGENTS.md

@@ -0,0 +1,52 @@
+# AGENTS.md — Operating Rules for All Agents on This Repo
+
+1. **Always read `.agent/PLAN.md` first.** It contains the architecture, the
+   LOCKED DECISIONS, the UI/UX standards, the data model, and the roadmap.
+   Do not design anything that contradicts it.
+2. **Follow the phased execution protocol in `.agent/phases/`.** Work through
+   `.agent/phases/todo/` in numeric order. When a phase is complete, move its
+   file to `.agent/phases/complete/`.
+3. **Strictly adhere to the LOCKED DECISIONS** (PLAN §2). If you believe a
+   LOCKED decision is wrong, stop and flag it — do not silently deviate.
+4. **"One Story, One Phase":** each user story in `.agent/user_stories/`
+   corresponds to a distinct execution phase that includes its own dedicated
+   Playwright E2E test suite (one test file per story, run in isolation).
+5. **"UI Structure Check":** before finalizing any UI component, verify that
+   it follows the layout principles in `.agent/PLAN.md` §7 (proper container
+   usage, centered 46rem chat column, full-width tables on Sources — no
+   skinny wasted-space lists) and meets WCAG 2.1 AA basics (semantic
+   landmarks, labels, contrast ≥4.5:1, focus-visible, aria-live for the
+   stream).
+6. **"No CDN Rule":** all CSS, JS, fonts, and images must be served statically
+   from within the FastAPI application. No `<script src="https://…">` or
+   `<link href="https://…">` tags in HTML templates unless bundled locally.
+   An integration test enforces this on the index page.
+7. **"Debugpy Check":** any new entrypoint must keep the conditional import —
+   `debugpy` is imported **only** when `DEBUGPY=1` (see
+   `app/core/debugging.py`); default off, never imported otherwise.
+8. **Git protocol:** Git is mandatory. One **atomic, professional commit per
+   completed phase** (Conventional Commits, e.g. `feat(rag): stream RAG
+   answers over SSE with source citations`). Always append `--no-gpg-sign`
+   (the repo also sets `commit.gpgsign=false`). `.agent/` is gitignored by
+   design — use `git add -f .agent/…` when a commit must record plan changes.
+9. **Test gates are non-negotiable:** a phase is complete only when unit +
+   integration tests pass, `app/` coverage is **>90%**
+   (`uv run pytest --cov=app --cov-report=term-missing`), and the phase's
+   Playwright E2E file passes **in isolation**
+   (`uv run pytest tests/e2e/test_<story>.py -v --no-cov`).
+10. **Amply log, visibly feed back:** server-side, log the required
+    per-turn line (PLAN §9); UI-side, honor the "never stale" feedback
+    contract (PLAN §7.4).
+
+## Quick reference
+```bash
+podman compose up -d db                      # start Postgres 17 + pgvector
+cp .env.example .env                         # once; then edit
+uv run alembic upgrade head                  # apply migrations
+uv run uvicorn app.main:app --reload         # dev server (add DEBUGPY=1 to debug)
+uv run pytest                                # unit + integration
+uv run pytest --cov=app --cov-report=term-missing
+uv run playwright install chromium           # once
+uv run pytest tests/e2e/test_smoke.py -v --no-cov
+uv run ruff check . && uv run pyright        # lint + types
+```