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>

app/api/admin/seed-template-embeddings/route.ts

@@ -1,5 +1,8 @@
 import { NextResponse } from 'next/server'
-import { seedAllTemplateEmbeddings, getSchemaVersion } from '@/lib/bookkeeping/template-embeddings'
+import { extensionRegistry } from '@/lib/extensions/registry'
+import { ensureInitialized } from '@/lib/init'
+
+ensureInitialized()
 
 export async function POST(request: Request) {
   const authHeader = request.headers.get('authorization')
@@ -9,14 +12,23 @@ export async function POST(request: Request) {
     return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
   }
 
+  const aiExt = extensionRegistry.get('ai-categorization')
+  if (!aiExt?.services?.seedAllTemplateEmbeddings || !aiExt?.services?.getSchemaVersion) {
+    return NextResponse.json(
+      { error: 'ai-categorization extension not loaded' },
+      { status: 503 }
+    )
+  }
+
   try {
-    const { seeded, errors } = await seedAllTemplateEmbeddings()
+    const { seeded, errors } = await aiExt.services.seedAllTemplateEmbeddings()
+    const schemaVersion = await aiExt.services.getSchemaVersion()
 
     return NextResponse.json({
       success: errors.length === 0,
       seeded,
       errors,
-      schema_version: getSchemaVersion(),
+      schema_version: schemaVersion,
     })
   } catch (error) {
     return NextResponse.json(