feat(selfhost): complete Supabase removal migration

Phase 1 — Pattern library
- Add src/lib/api.ts (typed PostgREST client, anon-key)
- Add src/lib/svc-fetch.ts (service-role fetch + PostgREST client)
- Add src/lib/db-types.ts (Database generic, RowOf helper)
- Add src/lib/auth-admin.ts (better-auth admin wrappers: createUser, listUsers, removeUser, requestPasswordReset, validateSession)

Phase 2 — Server action migration
- Migrate all 67 server actions off @supabase/supabase-js to svcApi/svcRpc
- Replace service.auth.admin.* with authAdmin.* (better-auth)
- Replace publicApi.auth.* with authAdmin.* (better-auth)
- Add typed single() null guards + nullable column fallbacks

Phase 3 — Delete mock data + debug routes
- Remove if(useMockData) branches from 7 files (-226 lines)
- Delete src/lib/mock-data.ts (no longer referenced)
- Delete 7 debug API routes (debug-admin-users, debug-auth, debug-cookie, debug-env, debug-get-admin-users, debug-hello, debug-me)

Phase 4 — Hard cut
- Delete src/lib/supabase.ts (orphan — no importers)
- Delete src/app/api/supabase + src/app/api/supabase-test routes
- Remove @supabase/ssr + @supabase/supabase-js from package.json
- Rename env vars: NEXT_PUBLIC_SUPABASE_URL → NEXT_PUBLIC_API_URL, NEXT_PUBLIC_SUPABASE_ANON_KEY → NEXT_PUBLIC_API_ANON_KEY, SUPABASE_SERVICE_ROLE_KEY → POSTGREST_SERVICE_KEY

Phase 5 — Verify
- npx tsc --noEmit: 0 errors
- npm run lint: 0 new errors from migration (104 pre-existing errors unrelated)
- npm run build: same failure mode as main worktree (PostgREST-dependent prerender), no regression

Net: 158 files changed, +1640 / -1903 lines (-263 net)

src/actions/shipping/fedex-labels.ts

@@ -58,8 +58,8 @@ async function getFedExTokenForCreate(
   brandId: string | null,
   adminUserId: string | null
 ): Promise<{ accessToken: string } | { error: string }> {
-  const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL!;
-  const supabaseKey = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!;
+  const supabaseUrl = process.env.NEXT_PUBLIC_API_URL!;
+  const supabaseKey = process.env.NEXT_PUBLIC_API_ANON_KEY!;
 
   // Try to get from shipping_settings
   const settingsRes = await fetch(
@@ -88,8 +88,8 @@ async function getFedExTokenForCreate(
 }
 
 async function isShipmentPerishable(orderId: string): Promise<boolean> {
-  const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL!;
-  const supabaseKey = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!;
+  const supabaseUrl = process.env.NEXT_PUBLIC_API_URL!;
+  const supabaseKey = process.env.NEXT_PUBLIC_API_ANON_KEY!;
 
   const res = await fetch(
     `${supabaseUrl}/rest/v1/rpc/get_order_items_perishable?p_order_id=${encodeURIComponent(orderId)}`,
@@ -128,8 +128,8 @@ export async function createFedExShipment(
     return { success: false, error: "Not authorized to create shipments" };
   }
 
-  const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL!;
-  const supabaseKey = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!;
+  const supabaseUrl = process.env.NEXT_PUBLIC_API_URL!;
+  const supabaseKey = process.env.NEXT_PUBLIC_API_ANON_KEY!;
 
   // Fetch order
   const orderRes = await fetch(