Add Svelte language support with SvelteKit framework resolver

- Add 'svelte' to Language type, DEFAULT_CONFIG includes, grammars, and config validation
- Add SvelteExtractor that extracts <script> blocks and delegates to TS/JS TreeSitterExtractor
- Add Svelte framework resolver for runes ($state, $derived, $effect, etc.), store auto-subscriptions, SvelteKit module aliases ($app/*, $env/*, $lib/*), and SvelteKit route detection
- Update README to list Svelte and Dart in supported languages

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

src/config.ts

@@ -54,6 +54,7 @@ export function validateConfig(config: unknown): config is CodeGraphConfig {
     'go',
     'rust',
     'java',
+    'svelte',
     'unknown',
   ];
   if (!c.languages.every((l) => validLanguages.includes(l as Language))) return false;