types: clear remaining tsc errors across 41 files (76→14, behavior-preserving)

Per-file type-only fixes surfaced after the Supabase client was correctly
typed. All fixes preserve runtime behavior; no any/ts-ignore/ts-expect-error.

- lib/supabase/client.ts: annotate the browser client as SupabaseClient<Database>
  (same ssr/js drift as server.ts; fixes it centrally for all callers).
- Supabase embedded-select joins whose FK metadata is missing from the
  generated types are bridged with `as unknown as <target>` + a TODO to remove
  after regenerating types/database.ts.
- setState optimistic-update variance and raw <select> enum values cast to the
  precise element/union type; .insert payload fields (Json, enums) given the
  precise column type via satisfies/field casts.
- Added narrowing guards where a value was legitimately nullable (comms channel,
  public form page) without changing the intended path.

The 14 remaining errors are confined to the four files fixed in Phase B (real
bugs + the tautological actions.test rewrite). 639 tests still green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/(app)/payments/page.tsx

@@ -1,3 +1,4 @@
+import type { ComponentProps } from 'react'
 import { createClient } from '@/lib/supabase/server'
 import { PaymentsClient } from './payments-client'
 
@@ -27,7 +28,7 @@ export default async function PaymentsPage() {
 
   return (
     <PaymentsClient
-      payments={payments ?? []}
+      payments={(payments ?? []) as ComponentProps<typeof PaymentsClient>['payments']}
       members={members ?? []}
       integrations={integrations ?? []}
       currentRole={member.role}