refactor: use ci-templates for tests, add dependabot

- Backend and frontend tests now call reusable workflows from
  voidreamer/ci-templates (test-python.yml, test-node.yml)
- Deploy workflows kept project-specific (terraform workspaces,
  config.js injection)
- Added dependabot for npm, pip, github-actions, terraform
- CI/CD reduced from 320 lines to 156 lines

Author: Merrino

.github/dependabot.yml

@@ -0,0 +1,39 @@
+version: 2
+updates:
+  - package-ecosystem: "npm"
+    directory: "/frontend"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "frontend"
+
+  - package-ecosystem: "pip"
+    directory: "/backend"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+    open-pull-requests-limit: 3
+    labels:
+      - "dependencies"
+      - "backend"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 3
+    labels:
+      - "dependencies"
+      - "ci"
+
+  - package-ecosystem: "terraform"
+    directory: "/terraform"
+    schedule:
+      interval: "monthly"
+    open-pull-requests-limit: 2
+    labels:
+      - "dependencies"
+      - "infra"