feat(prd-1): implement M3 - Forgejo CI workflows

- ci.yml: 3-job CI (test, prettier, typecheck) on grunt runner
- test-action.yml: agent-mode self-test (weekly + PR path triggers)
- upstream-sync.yml: weekly upstream check with labeled issue dedup
- Updated PRD checkboxes for M3 completion

Progress: 78% complete (7/9 milestones) - M8 (e2e testing) next

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

.forgejo/workflows/test-action.yml

@@ -0,0 +1,80 @@
+name: Test Action (Forgejo)
+
+on:
+  schedule:
+    # Weekly Monday at 06:00 UTC
+    - cron: "0 6 * * 1"
+  pull_request:
+    branches:
+      - main
+    paths:
+      - "src/**"
+      - "action.yml"
+      - ".forgejo/**"
+      - "base-action/**"
+  workflow_dispatch:
+
+concurrency:
+  group: test-action-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test-agent-mode:
+    name: Test Agent Mode on Forgejo
+    runs-on: grunt
+    steps:
+      - name: Checkout
+        uses: https://${{ secrets.READ_REPO_TOKEN }}@git.wxs.ro/xternal/checkout@v6.0.2
+        with:
+          fetch-depth: 1
+
+      - name: Run Claude Code Action (agent mode)
+        id: claude
+        uses: ./
+        with:
+          prompt: "Respond with exactly the text FORGEJO_PLATFORM_TEST_OK and nothing else. Do not use any tools."
+          claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
+          github_token: ${{ secrets.FORGEJO_CLAUDE_TOKEN }}
+          platform: "forgejo"
+        env:
+          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+
+      - name: Verify execution output exists
+        run: |
+          EXEC_FILE="${{ steps.claude.outputs.execution_file }}"
+          if [ -z "$EXEC_FILE" ]; then
+            echo "FAIL: execution_file output is empty"
+            exit 1
+          fi
+          if [ ! -f "$EXEC_FILE" ]; then
+            echo "FAIL: execution file does not exist at: $EXEC_FILE"
+            exit 1
+          fi
+          echo "OK: execution file exists at: $EXEC_FILE"
+
+          # Check that the output contains our test marker
+          if grep -q "FORGEJO_PLATFORM_TEST_OK" "$EXEC_FILE"; then
+            echo "OK: Output contains expected test marker"
+          else
+            echo "WARN: Test marker not found in output (Claude may have formatted differently)"
+            echo "--- Output contents (first 50 lines) ---"
+            head -50 "$EXEC_FILE"
+          fi
+
+      - name: Debug on failure
+        if: failure()
+        run: |
+          echo "=== Debug Info ==="
+          echo "Platform env: PLATFORM=$PLATFORM FORGEJO=$FORGEJO"
+          echo "Server URL: $GITHUB_SERVER_URL"
+          echo "API URL: $GITHUB_API_URL"
+          echo "Event: ${{ github.event_name }}"
+          echo "Actor: ${{ github.actor }}"
+          echo ""
+          EXEC_FILE="${{ steps.claude.outputs.execution_file }}"
+          if [ -f "$EXEC_FILE" ]; then
+            echo "--- Execution file contents ---"
+            cat "$EXEC_FILE"
+          else
+            echo "No execution file found"
+          fi