ci: let Dependabot watch the dependencies

The SHA-pinned actions, the two base images, the compose file, the Python project and the npm assets had no update stream, so a pinned reference only moved when someone noticed it by hand. Adds a daily Dependabot config for all five.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/dependabot.yml

@@ -0,0 +1,47 @@
+version: 2
+
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+      time: "00:00"
+    labels:
+      - "dependencies"
+      - "ci"
+
+  - package-ecosystem: "docker"
+    directory: "/"
+    schedule:
+      interval: "daily"
+      time: "00:00"
+    labels:
+      - "dependencies"
+      - "docker"
+
+  - package-ecosystem: "docker-compose"
+    directory: "/"
+    schedule:
+      interval: "daily"
+      time: "00:00"
+    labels:
+      - "dependencies"
+      - "docker"
+
+  - package-ecosystem: "pip"
+    directory: "/"
+    schedule:
+      interval: "daily"
+      time: "00:00"
+    labels:
+      - "dependencies"
+      - "python"
+
+  - package-ecosystem: "npm"
+    directory: "/app"
+    schedule:
+      interval: "daily"
+      time: "00:00"
+    labels:
+      - "dependencies"
+      - "javascript"