chore(security): add verified secret scanning

.github/workflows/secret-scan.yml

@@ -0,0 +1,63 @@
+name: "Security Gate: Secret Scanning"
+
+on:
+  push:
+    branches: ["**"]
+  pull_request:
+    branches: [main, master]
+
+permissions: {}
+
+jobs:
+  trufflehog:
+    name: Scan for Verified Secrets
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Resolve scan range
+        id: scan_range
+        env:
+          EVENT_NAME: ${{ github.event_name }}
+          PR_BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          PR_HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+          PUSH_BASE_SHA: ${{ github.event.before }}
+          PUSH_HEAD_SHA: ${{ github.sha }}
+          DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
+        run: |
+          set -euo pipefail
+          zero_sha="0000000000000000000000000000000000000000"
+
+          if [[ "$EVENT_NAME" == "pull_request" ]]; then
+            base="$PR_BASE_SHA"
+            head="$PR_HEAD_SHA"
+          else
+            base="$PUSH_BASE_SHA"
+            head="$PUSH_HEAD_SHA"
+            if [[ -z "$base" || "$base" == "$zero_sha" ]]; then
+              base="origin/$DEFAULT_BRANCH"
+            fi
+          fi
+
+          echo "base=$base" >> "$GITHUB_OUTPUT"
+          echo "head=$head" >> "$GITHUB_OUTPUT"
+
+      - name: TruffleHog OSS
+        id: trufflehog
+        uses: trufflesecurity/trufflehog@v3.95.2
+        with:
+          path: ./
+          base: ${{ steps.scan_range.outputs.base }}
+          head: ${{ steps.scan_range.outputs.head }}
+          extra_args: --only-verified --debug
+
+      - name: Notify on failure
+        if: steps.trufflehog.outcome == 'failure'
+        run: |
+          echo "::error::Verified secrets found. Rotate the credential before merging."
+          exit 1