feat(deploy): use external build + image instead of compose build

Build image separately with: docker build -t fireflyapi:latest .
Consistent with StarfireAPI deployment pattern.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

deploy/docker-compose.yml

@@ -2,9 +2,10 @@
 # FireflyAPI Docker Compose Configuration
 # =============================================================================
 # Quick Start:
-#   1. Copy .env.example to .env and configure
-#   2. docker-compose up -d --build
-#   3. Check logs: docker-compose logs -f fireflyapi
+#   1. Build image: docker build -t fireflyapi:latest .  (in project root)
+#   2. Copy .env.example to .env and configure
+#   3. docker-compose up -d
+#   4. Check logs: docker-compose logs -f fireflyapi
 #   4. Access: http://localhost:8080
 #
 # All configuration is done via environment variables.
@@ -16,9 +17,6 @@ services:
   # FireflyAPI Application
   # ===========================================================================
   fireflyapi:
-    build:
-      context: ..
-      dockerfile: Dockerfile
     image: fireflyapi:latest
     container_name: fireflyapi
     restart: unless-stopped