test(frontend): exclude mentionNodeView from server coverage (#628)

CI's node coverage run (vite.config.ts, 'measure utility + server-side logic
only') counts every .ts under the include globs via all-files, but the Tiptap
NodeView builds live ProseMirror DOM and only runs in the browser editor — it is
exercised by the client project's browser tests, not the node run. Left in, it
showed 0% and dragged global functions (78.68%) and branches (78.48%) below the
80% gate.

Exclude it alongside the .svelte / browser-only UI files this config already
measures around. Restores the gate: statements 88.82%, branches 82.3%,
functions 87.27%, lines 89.77% (server project, verified locally).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/vite.config.ts

@@ -74,7 +74,16 @@ export default defineConfig({
 				'src/lib/document/**',
 				'src/hooks.server.ts'
 			],
-			exclude: ['**/*.svelte', '**/*.svelte.ts', '**/__mocks__/**'],
+			exclude: [
+				'**/*.svelte',
+				'**/*.svelte.ts',
+				'**/__mocks__/**',
+				// Tiptap NodeView — builds live ProseMirror DOM and only runs inside
+				// the browser editor, so it is exercised by the client project's
+				// browser tests, not this node server-coverage run. Browser-only UI
+				// .ts file, excluded like the actions/hooks this config measures around.
+				'src/lib/shared/discussion/mentionNodeView.ts'
+			],
 			thresholds: {
 				lines: 80,
 				functions: 80,