Release v1.1.2: publish container image + add security workflows

- Bump VERSION to 1.1.2 (no app behavior change from 1.1.1).
- release.yml: add workflow_dispatch so images can be published manually from
  the Actions tab in addition to on version tags.
- Add CodeQL code scanning (Python + JavaScript), free for public repos.
- Add Dependabot config for GitHub Actions and pip updates.

This is the first release to publish a multi-arch image to GHCR
(ghcr.io/allennpit/ads-bit).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/dependabot.yml

@@ -0,0 +1,17 @@
+version: 2
+updates:
+  # Keep GitHub Actions pinned versions current.
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: weekly
+    commit-message:
+      prefix: "ci"
+
+  # Keep Python dependencies current.
+  - package-ecosystem: pip
+    directory: "/"
+    schedule:
+      interval: weekly
+    commit-message:
+      prefix: "deps"