refactor: remove extension toggle system — compiled-in extensions are always active (#59)

The runtime toggle system (extension_toggles table, API routes, hooks, UI components)
added unnecessary complexity. Extensions controlled via extensions.config.json at build
time are now always active for all users. This removes ~835 lines of toggle-related code
including API routes, DB queries, the ExtensionToggleButton component, useEnabledExtensions
and useExtensionToggle hooks, and the toggle-check module. AI consent gating remains
unchanged.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/extensions/index.ts

@@ -2,14 +2,9 @@ export { extensionRegistry } from './registry'
 export { loadExtensions } from './loader'
 export type {
   Extension,
-  RouteDefinition,
   ApiRouteDefinition,
-  SidebarItem,
-  ReportDefinition,
-  SettingsPanelDefinition,
-  TaxCodeDefinition,
-  DimensionDefinition,
   MappingRuleTypeDefinition,
   ExtensionEventHandler,
   ExtensionContext,
+  SettingsPanelDefinition,
 } from './types'