fix: resolve CI failures — Node 20+, exclude scanner-worker from build

- Update GitHub Actions workflows to Node 20/22 (ESLint 10 requires Node 20+)
- Exclude scanner-worker/ from frontend tsconfig and .dockerignore
- Update engines to require Node >= 20

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/workflows/backend.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [18, 20]
+        node-version: [20, 22]
 
     steps:
       - uses: actions/checkout@v4

.github/workflows/frontend.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [18, 20]
+        node-version: [20, 22]
 
     steps:
       - uses: actions/checkout@v4