feat: add Quart app factory, config loader, and /api/health endpoint

Config reads from env vars (12-factor); .env.example documents defaults.
Health endpoint is liveness-only (no DB/Redis touch). Test added for CI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.env.example

@@ -0,0 +1,24 @@
+# Database
+DB_USER=fabledcurator
+DB_PASSWORD=changeme_use_a_real_password
+DB_HOST=postgres
+DB_PORT=5432
+DB_NAME=fabledcurator
+
+# Redis / Celery
+CELERY_BROKER_URL=redis://redis:6379/0
+CELERY_RESULT_BACKEND=redis://redis:6379/0
+
+# App
+# Generate with: openssl rand -hex 32
+SECRET_KEY=changeme_32_byte_hex_secret
+
+# Extension API key — used in FC-3, lands later but reserved now
+# Generate with: openssl rand -hex 32
+EXTENSION_API_KEY=
+
+# Logging
+LOG_LEVEL=INFO
+
+# Deployment posture: plain HTTP (no TLS in the app; reverse proxy if needed)
+# See docs/superpowers/specs/2026-05-13-fabledcurator-merge-design.md §2.1