fix: resolve 8 dependabot security alerts + add automated dep mgmt

- go: upgrade gomarkdown/markdown (HIGH CVE-2026-40890)
- go: upgrade go-git/go-git/v5 v5.16.4 -> v5.18.0 (4 CVEs: #37/#33/#32/#22)
- npm: add postcss >=8.5.10 override (MEDIUM CVE-2026-41305)
- ci: add govulncheck job + sarif upload to security tab
- ci: add dependency-review workflow (blocks PRs with known vulns)
- ci: add dependabot-auto-merge for semver-patch/minor bumps
- chore: enable weekly dependabot for gomod, npm, github-actions
- chore: remove stale package-lock.json (bun.lockb is canonical)

Author: vuon9

.github/dependabot.yml

@@ -0,0 +1,18 @@
+version: 2
+updates:
+  - package-ecosystem: "gomod"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    vendor: true
+
+  - package-ecosystem: "npm"
+    directory: "/frontend"
+    schedule:
+      interval: "weekly"
+    versioning-strategy: increase
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/ci.yml

@@ -110,6 +110,37 @@ jobs:
           recreate: true
           path: code-coverage-results.md
 
+  govulncheck:
+    name: Go Vulnerability Check
+    needs: build
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      security-events: write
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: "1.25.0"
+          check-latest: true
+          cache: true
+          cache-dependency-path: go.sum
+
+      - name: Run govulncheck
+        run: |
+          go install golang.org/x/vuln/cmd/govulncheck@latest
+          govulncheck -format sarif ./... > govulncheck.sarif || true
+
+      - name: Upload govulncheck results
+        if: always()
+        uses: github/codeql-action/upload-sarif@v3
+        with:
+          sarif_file: govulncheck.sarif
+
   frontend-tests:
     name: Frontend Tests
     needs: build

.github/workflows/dependabot-auto-merge.yml

@@ -0,0 +1,21 @@
+name: Dependabot auto-merge
+on: pull_request
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  dependabot:
+    runs-on: ubuntu-latest
+    if: github.event.pull_request.user.login == 'dependabot[bot]'
+    steps:
+      - name: Dependabot metadata
+        id: metadata
+        uses: dependabot/fetch-metadata@v2
+      - name: Enable auto-merge for Dependabot PRs
+        if: steps.metadata.outputs.update-type == 'version-update:semver-patch' || steps.metadata.outputs.update-type == 'version-update:semver-minor'
+        run: gh pr merge --auto --merge "$PR_URL"
+        env:
+          PR_URL: ${{github.event.pull_request.html_url}}
+          GH_TOKEN: ${{secrets.GITHUB_TOKEN}}

.github/workflows/dependency-review.yml

@@ -0,0 +1,14 @@
+name: Dependency Review
+on: pull_request
+
+permissions:
+  contents: read
+
+jobs:
+  dependency-review:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Dependency Review
+        uses: actions/dependency-review-action@v4

.gitignore

@@ -18,3 +18,4 @@ frontend/test-results/
 test-results/
 frontend/playwright-report/
 playwright-report/
+package-lock.json