Remove unused SidebarField; add CI typecheck job before client Docker build

- Delete the now-unused SidebarField component from TicketDetail.tsx
- Add typecheck-client CI job that runs tsc --noEmit on the client before
  the Docker build, so TypeScript errors surface fast with a clear message
- build-client now depends on typecheck-client passing

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

.gitea/workflows/build.yml

@@ -10,6 +10,28 @@ env:
   OWNER: ${{ github.repository_owner }}
 
 jobs:
+  typecheck-client:
+    name: TypeScript Check (client)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: '22'
+          cache: 'npm'
+          cache-dependency-path: client/package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+        working-directory: ./client
+
+      - name: Type check
+        run: npx tsc --noEmit
+        working-directory: ./client
+
   build-server:
     name: Build Server
     runs-on: ubuntu-latest
@@ -38,6 +60,7 @@ jobs:
 
   build-client:
     name: Build Client
+    needs: typecheck-client
     runs-on: ubuntu-latest
     steps:
       - name: Checkout