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/(app)/ops/[id]/kb-entry-editor.tsx

@@ -96,7 +96,7 @@ export default function KbEntryEditor({ entry, member }: Props) {
                 <label className="font-sans text-xs font-medium text-muted-foreground block mb-1.5">Visibility</label>
                 <select
                   value={visibility}
-                  onChange={e => setVisibility(e.target.value)}
+                  onChange={e => setVisibility(e.target.value as 'board' | 'all_members' | 'admin_only')}
                   className="w-full bg-background border border-border rounded px-3 py-2 font-sans text-sm text-foreground focus:outline-none focus:border-primary transition"
                 >
                   <option value="all_members">All Members</option>