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/app/api/wholesale/price-sheet/route.ts

@@ -39,8 +39,8 @@ export async function POST(req: NextRequest) {
     return NextResponse.json({ error: "customerIds array and brandId are required" }, { status: 400 });
   }
 
-  const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL!;
-  const supabaseKey = process.env.SUPABASE_SERVICE_ROLE_KEY!;
+  const supabaseUrl = process.env.NEXT_PUBLIC_API_URL!;
+  const supabaseKey = process.env.POSTGREST_SERVICE_KEY!;
 
   // Fetch brand settings for branding + pickup location
   const settings = await getWholesaleSettings(effectiveBrandId);
@@ -179,7 +179,7 @@ ${hasCustomNote ? `      <p style="margin: 0 0 12px; color: #1e293b; font-size:
   }
 
   // Fire-and-forget trigger to process the queue
-  fetch(`${process.env.NEXT_PUBLIC_SUPABASE_URL!}/api/wholesale/notifications/send`, {
+  fetch(`${process.env.NEXT_PUBLIC_API_URL!}/api/wholesale/notifications/send`, {
     method: "POST",
     headers: { "Content-Type": "application/json" },
   }).catch(() => {});