fix(frontend): add sentrySvelteKit Vite plugin for source map upload

Adds the sentrySvelteKit() Vite plugin as the first plugin in vite.config.ts.
When SENTRY_AUTH_TOKEN is set at build time, source maps are uploaded to
GlitchTip so error stack traces show original TypeScript source and line number.
When SENTRY_AUTH_TOKEN is absent (CI, dev builds), upload is disabled via
autoUploadSourceMaps: false — the build succeeds normally.

Resolves Felix's review blocker on PR #591.

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

.env.example

@@ -52,6 +52,8 @@ GLITCHTIP_SECRET_KEY=changeme-generate-a-real-secret
 SENTRY_DSN=
 # VITE_SENTRY_DSN: frontend (SvelteKit) — injected at build time via Vite
 VITE_SENTRY_DSN=
+# Sentry/GlitchTip auth token for source map upload at build time (optional)
+SENTRY_AUTH_TOKEN=
 
 # Production SMTP — uncomment and fill in to send real emails instead of catching them
 # APP_BASE_URL=https://your-domain.example.com

frontend/vite.config.ts

@@ -1,3 +1,4 @@
+import { sentrySvelteKit } from '@sentry/sveltekit';
 import { paraglideVitePlugin } from '@inlang/paraglide-js';
 import devtoolsJson from 'vite-plugin-devtools-json';
 import tailwindcss from '@tailwindcss/vite';
@@ -33,6 +34,21 @@ export default defineConfig({
 		}
 	},
 	plugins: [
+		sentrySvelteKit({
+			org: 'familienarchiv',
+			project: 'frontend',
+			authToken: process.env.SENTRY_AUTH_TOKEN,
+			sentryUrl: (() => {
+				const dsn = process.env.VITE_SENTRY_DSN;
+				if (!dsn) return undefined;
+				try {
+					return new URL(dsn).origin;
+				} catch {
+					return undefined;
+				}
+			})(),
+			autoUploadSourceMaps: !!process.env.SENTRY_AUTH_TOKEN
+		}),
 		tailwindcss(),
 		sveltekit(),
 		devtoolsJson(),