chore: add .env.example and wire compose.yml to env vars

- .env.example documents all env vars with defaults (postgres creds, DATABASE_URL, TTLs, pool sizes)
- compose.yml reads postgres credentials and app config from .env via env_file
- .gitignore: track .env.example, ignore .env

.env.example

@@ -0,0 +1,18 @@
+# PostgreSQL
+POSTGRES_DB=goyomi
+POSTGRES_USER=goyomi
+POSTGRES_PASSWORD=goyomi
+
+# App
+DATABASE_URL=postgres://goyomi:goyomi@postgres:5432/goyomi?sslmode=disable
+FLARESOLVERR_URL=http://flaresolverr:8191
+ADDR=:8080
+
+# Connection pool
+DB_MAX_CONNS=10
+DB_MIN_CONNS=2
+
+# Cache TTLs (seconds)
+MANGA_LIST_TTL_SECONDS=600
+MANGA_DETAIL_TTL_SECONDS=3600
+CHAPTER_LIST_TTL_SECONDS=600