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) <[email protected]>

app/api/stripe/webhook/[space]/route.ts

@@ -265,15 +265,18 @@ export async function POST(
           .eq('external_id', inv.id)
           .maybeSingle()
         if (!dupe) {
-          await admin.from('payments').insert(
-            stripeInvoiceToPaymentRow({
-              inv,
-              spaceId,
-              memberId,
-              eventId: event.id,
-              nowIso: new Date().toISOString(),
-            }),
-          )
+          const paymentRow = stripeInvoiceToPaymentRow({
+            inv,
+            spaceId,
+            memberId,
+            eventId: event.id,
+            nowIso: new Date().toISOString(),
+          })
+          await admin.from('payments').insert({
+            ...paymentRow,
+            status: paymentRow.status as 'linked' | 'unlinked',
+            link_status: paymentRow.link_status as 'linked' | 'unlinked',
+          })
         }
         if (memberId) {
           await admin