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)

.env.example

@@ -0,0 +1,31 @@
+# Brain of Reese — environment configuration
+# Copy to `.env` and adjust:  cp .env.example .env
+# (`.env` is gitignored; never commit secrets.)
+
+# --- App ---
+BOR_ENVIRONMENT=development
+# BOR_LOG_LEVEL=INFO
+# BOR_STATIC_DIR=frontend          # dev default; container sets /app/static
+
+# --- Database (matches `podman compose` db service) ---
+BOR_DATABASE_URL=postgresql+psycopg://reese:reese@localhost:5432/brain_of_reese
+
+# --- LLM (self-hosted, OpenAI-compatible "aipi") ---
+BOR_LLM_BASE_URL=https://aipi.reeseapps.com/v1
+BOR_LLM_API_KEY=                  # falls back to $AIPI_KEY, then "not-needed"
+BOR_LLM_CHAT_MODEL=turbo
+BOR_LLM_EMBED_MODEL=embed
+BOR_EMBEDDING_DIM=768             # verified 2026-08 via scripts/llm_probe.py
+
+# --- RAG tuning ---
+BOR_TOP_K_CHUNKS=4
+BOR_TOP_N_DOCS=2
+BOR_RELEVANCE_THRESHOLD=0.30      # max cosine similarity required to answer (else honest deflection)
+BOR_MAX_CONTEXT_CHARS=24000       # cap on total document text sent to the LLM
+BOR_CHUNK_TARGET_CHARS=2000
+BOR_CHUNK_OVERLAP_CHARS=200
+BOR_EMBED_BATCH_SIZE=16
+
+# --- Debugging (0/1 — 1 enables attach-on-demand debugpy on port 5678) ---
+DEBUGPY=0
+# DEBUGPY_PORT=5678