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/__tests__/toggle-check.test.ts

@@ -1,48 +0,0 @@
-import { describe, it, expect, vi, beforeEach } from 'vitest'
-import { createMockSupabase } from '@/tests/helpers'
-
-const { supabase: mockSupabase, mockResult } = createMockSupabase()
-vi.mock('@/lib/supabase/server', () => ({
-  createServiceClient: () => Promise.resolve(mockSupabase),
-}))
-
-import { isExtensionEnabled } from '../toggle-check'
-
-describe('isExtensionEnabled', () => {
-  beforeEach(() => {
-    vi.clearAllMocks()
-  })
-
-  it('returns true when toggle exists and is enabled', async () => {
-    mockResult({ data: { enabled: true }, error: null })
-
-    const result = await isExtensionEnabled('user-1', 'general', 'receipt-ocr')
-
-    expect(result).toBe(true)
-    expect(mockSupabase.from).toHaveBeenCalledWith('extension_toggles')
-  })
-
-  it('returns false when toggle exists and is disabled', async () => {
-    mockResult({ data: { enabled: false }, error: null })
-
-    const result = await isExtensionEnabled('user-1', 'general', 'receipt-ocr')
-
-    expect(result).toBe(false)
-  })
-
-  it('returns true for legacy general extensions when no toggle row exists', async () => {
-    mockResult({ data: null, error: null })
-
-    const result = await isExtensionEnabled('user-1', 'general', 'receipt-ocr')
-
-    expect(result).toBe(true)
-  })
-
-  it('returns false for non-legacy extensions when no toggle row exists', async () => {
-    mockResult({ data: null, error: null })
-
-    const result = await isExtensionEnabled('user-1', 'restaurant', 'tip-tracking')
-
-    expect(result).toBe(false)
-  })
-})