feat(auth): phase 3 — replace Supabase GoTrue with bcryptjs+jose

Custom auth stack: bcryptjs password hashing (cost 10, GoTrue-compatible),
jose JWT session cookies (edge-safe, 8hr TTL), new API routes for
login/logout/reset/change-password, middleware rewritten to JWT-only
verification with no DB access. All 38 protected pages and API routes
migrated from supabase.auth.getUser() to getSession(). Supabase .from()
queries retained for Phase 4. lib/db/index.ts refactored to lazy Proxy
singleton to avoid module-level throw during Next.js build.

tsc: clean, build: clean, tests: 4/4 passed

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

lib/auth/require-admin.ts

@@ -1,18 +1,12 @@
-import { createClient } from '@/lib/supabase/server'
-import type { SupabaseClient } from '@supabase/supabase-js'
-import type { User } from '@supabase/supabase-js'
+import { getSession } from '@/lib/auth/get-session'
+import type { SessionPayload } from '@/lib/auth/session'
 
 // Shared guard for /api/admin/* routes: resolves the session and requires
-// the admin role. Returns user: null when the caller must respond 403.
+// the admin role. Returns session: null when the caller must respond 403.
 export async function requireAdmin(): Promise<{
-  supabase: SupabaseClient
-  user: User | null
+  session: SessionPayload | null
 }> {
-  const supabase = await createClient()
-  const { data: { user }, error } = await supabase.auth.getUser()
-  if (error || !user) return { supabase, user: null }
-  const { data: profile } = await supabase
-    .from('users').select('role').eq('id', user.id).single()
-  if (!profile || profile.role !== 'admin') return { supabase, user: null }
-  return { supabase, user }
+  const session = await getSession()
+  if (!session || session.role !== 'admin') return { session: null }
+  return { session }
 }