Support Immich URL/API key via docker-compose env vars

docker-compose.yml is tracked in a repo meant for publishing, so it can't
hold a real API key. Renamed it to docker-compose.yml.example (placeholder
values, safe to commit) and gitignored the real docker-compose.yml --
deploying is now "cp the example, fill in real values, docker compose up",
no .env file needed.

config.load() now reads IMMICH_URL/IMMICH_API_KEY from the environment
and applies them on top of whatever's in config.json, so setting them in
the compose file's environment: block takes effect without ever touching
the web UI. Env vars always win over the UI-saved values when both are
present -- verified they survive a save() with different UI-entered
values still in place.

server/app/config.py

@@ -28,8 +28,21 @@ class FrameConfig(BaseModel):
 def load() -> FrameConfig:
     with _lock:
         if not CONFIG_PATH.exists():
-            return FrameConfig()
-        return FrameConfig(**json.loads(CONFIG_PATH.read_text()))
+            cfg = FrameConfig()
+        else:
+            cfg = FrameConfig(**json.loads(CONFIG_PATH.read_text()))
+
+    # IMMICH_URL/IMMICH_API_KEY set in the environment (e.g. docker-compose.yml,
+    # see docker-compose.yml.example) take precedence over whatever's saved
+    # in CONFIG_PATH, so credentials never need to go through the web UI.
+    env_url = os.environ.get("IMMICH_URL")
+    env_key = os.environ.get("IMMICH_API_KEY")
+    if env_url:
+        cfg.immich_url = env_url
+    if env_key:
+        cfg.immich_api_key = env_key
+
+    return cfg
 
 
 def save(cfg: FrameConfig) -> None: