ci: add CodeQL, dependency-review, dependabot

- CodeQL: Go analysis, weekly Monday schedule
- dependency-review: block high-severity deps on PRs
- dependabot: weekly updates for github-actions and gomod

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

Author: syscod3

.github/dependabot.yml

@@ -0,0 +1,14 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+    labels: [dependencies, github-actions]
+
+  - package-ecosystem: gomod
+    directory: /
+    schedule:
+      interval: weekly
+    open-pull-requests-limit: 5
+    labels: [dependencies, go]

.github/workflows/codeql.yml

@@ -0,0 +1,27 @@
+name: CodeQL
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  schedule:
+    - cron: "0 2 * * 1"   # Monday 02:00 UTC
+
+permissions:
+  actions: read
+  contents: read
+  security-events: write
+
+jobs:
+  analyze:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: github/codeql-action/init@v3
+        with:
+          languages: go
+
+      - uses: github/codeql-action/autobuild@v3
+
+      - uses: github/codeql-action/analyze@v3

.github/workflows/dependency-review.yml

@@ -0,0 +1,19 @@
+name: Dependency Review
+
+on:
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  review:
+    runs-on: ubuntu-latest
+    if: github.actor != 'dependabot[bot]'
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/dependency-review-action@v4
+        with:
+          fail-on-severity: high