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)

.agent/phases/todo/07_story_responsive_polish.md

@@ -0,0 +1,57 @@
+# Phase 07 — Story: Responsive, Polished, Accessible UI
+
+**Story:** `.agent/user_stories/responsive-polish.md`
+**Context:** `.agent/PLAN.md` §7 (the whole UI/UX strategy)
+
+## Goal
+The final visual + accessibility audit pass across chat and Sources. No
+new features — enforce PLAN §7 end-to-end and fix every deviation.
+
+## Implementation steps
+1. Viewport sweep (360 / 375 / 768 / 1280 / 1600) on both pages: fix
+   overflow, pinched columns, dead whitespace. Chat column stays ≤46rem
+   centered; Sources table full-width with horizontal scroll <640px.
+2. A11y sweep (both pages): landmarks, skip link, labels on every input,
+   `aria-label` on every icon-only control, `:focus-visible` outline on
+   every focusable, `aria-live` regions intact, no contrast <4.5:1
+   (compute, don't eyeball — use the E2E helper).
+3. Reduced-motion + long-content pass (60-char paths, long answers).
+4. No-CDN re-verification on **both** pages (extend the integration test
+   to `/sources.html` if it only covers `/`).
+5. Final README polish pass: screenshots section (optional), quickstart
+   sanity, "Update your documents" workflow prominent.
+
+## UI Verification
+This phase IS the verification: the E2E below is the acceptance test.
+Additionally, manual screenshot pass at 1280px + 375px for both pages,
+reviewed against PLAN §7.1–7.4 before committing.
+
+## Testing & Quality
+- Integration: no-CDN check extended to Sources page; health unchanged.
+- Coverage: **>90%** on `app/` (final state of the whole app).
+- Whole suite green: `uv run pytest` (unit+integration) — the entire
+  repo must be green at this phase.
+
+## Playwright Execution Phase
+Run ONLY this story's suite:
+
+```bash
+uv run pytest tests/e2e/test_responsive_polish.py -v --no-cov
+```
+
+Implements the story mapping: no horizontal overflow at 5 viewports (both
+pages); chat column capped + centered at 1600px; Sources table ≥80%
+container at 1280px; landmarks/labels/skip-link sweep; WCAG contrast
+pairs ≥4.5:1 (computed); reduced-motion honored.
+
+## Success criteria
+- [ ] all six mapping tests pass at every viewport
+- [ ] zero known a11y deviations against PLAN §7.2
+- [ ] whole pytest suite green + coverage >90%
+- [ ] README polished
+- [ ] committed (this commit marks v1.0 feature-complete)
+
+## Commit
+```bash
+git add -A && git commit --no-gpg-sign -m "feat(ui): responsive + WCAG AA polish pass across chat and sources — v1 feature complete"
+```