refactor: consolidate extension system to general-only with manifest-driven architecture

- Remove all sector-specific extensions (construction, ecommerce, export,
  hotel, restaurant, tech) — only general-purpose extensions remain
- Move NE-bilaga and SRU export from extensions to core reports (lib/reports/)
- Move moms-box-mapping from extensions/export/shared to lib/vat/
- Replace per-extension API routes with catch-all dispatcher
  (app/api/extensions/ext/[...path]/route.ts)
- Add manifest.json for each extension with metadata, env vars, and deps
- Add api-routes.ts pattern for extension-defined API endpoints
- Add code generation scripts (generate-extension-registry, create-extension)
- Add extensions.config.json for opt-in extension loading
- Add extensions.schema.json for config validation
- Add email service interface with noop default (lib/email/service.ts)
- Add CI workflow (core-build.yml) to verify core builds with zero extensions
- Add migration 045: expand account_type CHECK for untaxed_reserves
- Update CLAUDE.md with comprehensive extension system documentation
- Update all report engines and bookkeeping services for new imports
- Clean up extensions.schema.json to only list existing extensions

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

components/chat/useChatStream.ts

@@ -60,7 +60,7 @@ export function useChatStream(options: UseChatStreamOptions = {}): UseChatStream
     try {
       abortControllerRef.current = new AbortController()
 
-      const response = await fetch('/api/extensions/ai-chat/stream', {
+      const response = await fetch('/api/extensions/ext/ai-chat/stream', {
         method: 'POST',
         headers: {
           'Content-Type': 'application/json',
@@ -175,7 +175,7 @@ export function useChatStream(options: UseChatStreamOptions = {}): UseChatStream
     setError(null)
 
     try {
-      const response = await fetch(`/api/extensions/ai-chat/sessions/${id}`)
+      const response = await fetch(`/api/extensions/ext/ai-chat/sessions/${id}`)
       if (!response.ok) {
         throw new Error('Failed to load session')
       }