feat: add composite action for clean distribution

- .gitea/actions/review/action.yml: composite action with caching
  Consumers just use:
    uses: https://gitea.weiker.me/rodin/review-bot/.gitea/actions/review@v0.1.0
  No Go toolchain needed, binary cached by version tag.

- Remove install.sh (replaced by composite action)
- CI workflow: use matrix strategy to parallelize reviews
- Self-review still builds from source (pre-release)

.gitea/workflows/ci.yml

@@ -18,35 +18,34 @@ jobs:
       - run: go vet ./...
       - run: go build -o review-bot ./cmd/review-bot
 
+  # Self-review: builds from source since we're pre-release
   review:
     runs-on: ubuntu-24.04
     if: github.event_name == 'pull_request'
     needs: test
+    strategy:
+      matrix:
+        include:
+          - name: sonnet
+            token_secret: SONNET_REVIEW_TOKEN
+            model: gpt-5
+          - name: gpt
+            token_secret: GPT_REVIEW_TOKEN
+            model: gpt-5-mini
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5
         with:
           go-version: '1.26'
       - run: go build -o review-bot ./cmd/review-bot
-      - name: Run Sonnet Review
+      - name: Run ${{ matrix.name }} review
         env:
           GITEA_URL: ${{ github.server_url }}
           GITEA_REPO: ${{ github.repository }}
           PR_NUMBER: ${{ github.event.pull_request.number }}
-          REVIEWER_TOKEN: ${{ secrets.SONNET_REVIEW_TOKEN }}
+          REVIEWER_TOKEN: ${{ secrets[matrix.token_secret] }}
           LLM_BASE_URL: ${{ secrets.LLM_BASE_URL }}
           LLM_API_KEY: ${{ secrets.LLM_API_KEY }}
-          LLM_MODEL: "gpt-5"
-          CONVENTIONS_FILE: "CONVENTIONS.md"
-        run: ./review-bot
-      - name: Run GPT Review
-        env:
-          GITEA_URL: ${{ github.server_url }}
-          GITEA_REPO: ${{ github.repository }}
-          PR_NUMBER: ${{ github.event.pull_request.number }}
-          REVIEWER_TOKEN: ${{ secrets.GPT_REVIEW_TOKEN }}
-          LLM_BASE_URL: ${{ secrets.LLM_BASE_URL }}
-          LLM_API_KEY: ${{ secrets.LLM_API_KEY }}
-          LLM_MODEL: "gpt-5-mini"
+          LLM_MODEL: ${{ matrix.model }}
           CONVENTIONS_FILE: "CONVENTIONS.md"
         run: ./review-bot