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>

lib/extensions/_generated/enabled-extensions.ts

@@ -0,0 +1,4 @@
+// AUTO-GENERATED — do not edit. Run `npm run setup:extensions` to regenerate.
+
+export const ENABLED_EXTENSION_IDS: ReadonlySet<string> = new Set([
+])

lib/extensions/_generated/extension-list.ts

@@ -0,0 +1,5 @@
+// AUTO-GENERATED — do not edit. Run `npm run setup:extensions` to regenerate.
+import type { Extension } from '../types'
+
+export const FIRST_PARTY_EXTENSIONS: Extension[] = [
+]

lib/extensions/_generated/sector-definitions.ts

@@ -0,0 +1,5 @@
+// AUTO-GENERATED — do not edit. Run `npm run setup:extensions` to regenerate.
+import type { ExtensionDefinition } from '../types'
+
+export const EXTENSION_DEFINITIONS: Record<string, ExtensionDefinition[]> = {
+}

lib/extensions/_generated/workspace-map.tsx

@@ -0,0 +1,7 @@
+// AUTO-GENERATED — do not edit. Run `npm run setup:extensions` to regenerate.
+import dynamic from 'next/dynamic'
+import type { ComponentType } from 'react'
+import type { WorkspaceComponentProps } from '../workspace-registry'
+
+export const WORKSPACES: Record<string, ComponentType<WorkspaceComponentProps>> = {
+}