ci: add release + validation workflows

- release.yml: on v* tag, build Chrome + Firefox zips, compute
  SHA256, upload artifacts, attach to GitHub Release with auto
  generated notes
- ci.yml: on PR/master push, validate manifest JSON, enforce
  version parity, build, web-ext lint Firefox bundle

.github/workflows/ci.yml

@@ -0,0 +1,32 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Validate manifest JSON
+        run: |
+          python3 -c "import json,sys; json.load(open('manifest.json'))"
+          python3 -c "import json,sys; json.load(open('manifest.firefox.json'))"
+
+      - name: Manifest versions must match
+        run: |
+          C=$(python3 -c "import json; print(json.load(open('manifest.json'))['version'])")
+          F=$(python3 -c "import json; print(json.load(open('manifest.firefox.json'))['version'])")
+          [ "$C" = "$F" ] || { echo "Chrome=$C Firefox=$F"; exit 1; }
+
+      - name: Build runs cleanly
+        run: bash scripts/build.sh
+
+      - name: Install web-ext
+        run: npm install -g web-ext
+
+      - name: web-ext lint (Firefox)
+        run: web-ext lint --source-dir dist/firefox --self-hosted

.github/workflows/release.yml

@@ -0,0 +1,71 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*"
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: "Tag to build (e.g. v2.1.0). Leave blank to build current ref."
+        required: false
+
+permissions:
+  contents: write
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.inputs.tag || github.ref }}
+
+      - name: Read version from manifest
+        id: meta
+        run: |
+          VERSION=$(grep '"version"' manifest.json | head -1 | sed 's/.*: *"\([^"]*\)".*/\1/')
+          echo "version=$VERSION" >> "$GITHUB_OUTPUT"
+          echo "tag=v$VERSION" >> "$GITHUB_OUTPUT"
+
+      - name: Verify tag matches manifest version
+        if: startsWith(github.ref, 'refs/tags/v')
+        run: |
+          TAG="${GITHUB_REF#refs/tags/}"
+          if [ "$TAG" != "${{ steps.meta.outputs.tag }}" ] && [ "$TAG" != "${{ steps.meta.outputs.tag }}-firefox" ]; then
+            echo "Tag $TAG does not match manifest version ${{ steps.meta.outputs.tag }}"
+            exit 1
+          fi
+
+      - name: Build Chrome + Firefox zips
+        run: bash scripts/build.sh
+
+      - name: Compute checksums
+        working-directory: dist
+        run: |
+          shasum -a 256 keyfinder-v${{ steps.meta.outputs.version }}-chrome.zip > keyfinder-v${{ steps.meta.outputs.version }}-chrome.zip.sha256
+          shasum -a 256 keyfinder-v${{ steps.meta.outputs.version }}-firefox.zip > keyfinder-v${{ steps.meta.outputs.version }}-firefox.zip.sha256
+
+      - name: Upload build artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: keyfinder-v${{ steps.meta.outputs.version }}
+          path: |
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-chrome.zip
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-firefox.zip
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-chrome.zip.sha256
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-firefox.zip.sha256
+          if-no-files-found: error
+
+      - name: Attach to GitHub Release
+        if: startsWith(github.ref, 'refs/tags/v')
+        uses: softprops/action-gh-release@v2
+        with:
+          files: |
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-chrome.zip
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-firefox.zip
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-chrome.zip.sha256
+            dist/keyfinder-v${{ steps.meta.outputs.version }}-firefox.zip.sha256
+          generate_release_notes: true
+          fail_on_unmatched_files: true