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]>

lib/secrets/vault.ts

@@ -4,6 +4,7 @@
 // module: it takes a Supabase admin client and is imported by server actions
 // and route handlers. Secrets are server-only and never returned to a client.
 import type { createAdminClient } from '@/lib/supabase/admin'
+import type { TablesInsert } from '@/types/database'
 import { encryptSecret, decryptSecret, encryptionAvailable } from '@/lib/secrets/crypto'
 
 type Admin = ReturnType<typeof createAdminClient>
@@ -33,7 +34,11 @@ export async function storeSecret(
     row.value = value
     row.encryption_version = 0
   }
-  const { data, error } = await admin.from('secrets').insert(row).select('id').single()
+  const { data, error } = await admin
+    .from('secrets')
+    .insert(row as TablesInsert<'secrets'>)
+    .select('id')
+    .single()
   if (error || !data) return null
   return data.id as string
 }