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/user_stories/suggestion-chips.md

@@ -0,0 +1,58 @@
+# Story: Suggestion Chips
+
+**Phase:** `05_story_suggestion_chips.md` · **E2E:** `tests/e2e/test_suggestion_chips.py`
+
+## Narrative
+
+As **a user who opens the chat for the first time** (or after a deflection),
+I want a few **concrete example questions** right in front of me — so I
+immediately understand what Brain is good at and can start with zero
+friction.
+
+- **Given** I land on the chat page
+- **When** the app is healthy
+- **Then** I see 3–4 suggestion chips drawn from `GET /api/suggestions`
+  (defaults in settings, tuned to the real Homelab topics), and clicking one
+  fills the composer and submits it.
+
+## Acceptance criteria
+1. `GET /api/suggestions` returns the configured list (settings-driven,
+   overridable via `BOR_SUGGESTIONS` JSON env).
+2. Chips render in the empty state as `<button class="suggestion-chip">`
+   (real buttons, not links/divs) with `role="list"` container +
+   `role="listitem"` items; `aria-label="Suggested questions"` on the group.
+3. Click behavior: fills `#message-input`, focuses it, **and submits**
+   (one tap → answer). Keyboard: Tab to chip, Enter activates.
+4. After the first user message the empty state (and its chips) is replaced
+   by the conversation; chips re-appear only on deflection (see
+   honest-deflection story).
+5. If `/api/suggestions` fails, the chat still works (progressive
+   enhancement — no chips, no error spam).
+6. Mobile: chips become a horizontally scrollable single row
+   (no wrapping into the composer's territory).
+
+## UI Visualization & Structure
+- Chips: pill (`border-radius: 999px`), `bg --brand-soft`, `text --brand-ink`
+  (≥6:1), 1px `--line` border, **min-height 44px**, comfortable
+  `padding 0.55rem 1rem`; hover deepens bg; `:active` scales 0.98.
+- Desktop: `flex-wrap: wrap`, centered under the empty-state subcopy, gap 0.5rem.
+- Mobile (≤640px): `flex-wrap: nowrap; overflow-x: auto` single row,
+  `scrollbar-width: thin`, chips `flex: 0 0 auto` (thumb-friendly, no
+  accidental double-tap on wrapped lines).
+- Default suggestion copy (tune to real docs in this phase):
+  1. "How is my Kubernetes cluster set up?"
+  2. "What's my backup strategy?"
+  3. "How do I deploy a new service?"
+  4. "What's currently running in the homelab?"
+
+## Playwright Mapping Rule
+**Test Scenario → `tests/e2e/test_suggestion_chips.py`**:
+1. `test_onboarding_chips_render` — goto `/`, assert ≥3 `.suggestion-chip`
+   visible inside `#suggestions` (role=list) with non-empty text.
+2. `test_chip_click_submits` — click the first chip; assert a user bubble
+   with the chip's exact text appears and the brain reply (mock) follows.
+3. `test_chips_keyboard_accessible` — Tab from the page start reaches the
+   first chip; Enter submits it.
+4. `test_chips_mobile_row` — at 375px viewport, the chip row is
+   horizontally scrollable (`scrollWidth > clientWidth` or single-line
+   height check) and no chip is cut vertically.