fix(.gitignore): Properly ignore entire wwwroot directory

Root cause of CI/CD failure: .gitignore only ignored specific files
(assets/, index.html) but not the directory itself, causing:
- Directory exists in git checkout
- rm -rf fails due to git ownership issues
- CI/CD copy step hangs or fails

Solution: Ignore the entire src/KArtSell.Host/wwwroot/ directory
so it never exists in git checkout, allowing CI to create it fresh.

This is the actual fix for "Build frontend into Host static assets" failure.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.gitignore

@@ -4,11 +4,10 @@ frontend/node_modules/
 frontend/dist/
 frontend/.env.local
 # Vite build output copied into the Host's wwwroot by KArtSell.Host.csproj's
-# BuildFrontend target (local dev) and by .gitea/workflows/deploy.yml (production).
+# BuildFrontend target (local dev) and by .gitea/workflows/ci.yml (CI/CD).
 # Content-hashed filenames change on every rebuild even with no source changes,
-# so this must never be committed -- see CURRENT_ROADMAP.md item #3.
-src/KArtSell.Host/wwwroot/assets/
-src/KArtSell.Host/wwwroot/index.html
+# so this must never be committed -- see CLAUDE.md #3.
+src/KArtSell.Host/wwwroot/
 frontend/test-results/
 .playwright/
 TestResults/