fix(activity): tolerate unknown activity kinds in ActivityFeed

The live-tail stream (now reachable through the new Vite /api proxy)
started delivering activity rows with kind="manual_match", a kind the
ActivityFeed kindConfig map didn't know about. The map lookup returned
undefined, and reading .icon on it threw — taking the whole Activity
Log page down.

Two fixes:

1. Add "manual_match" to the ActivityKind union in src/types/index.ts
   and to the kindConfig map in src/components/ActivityFeed.tsx (with
   a Wrench icon + neutral tone), so the kind is properly typed and
   rendered.

2. Add a FALLBACK_KIND guard so any future backend-emitted kind that
   arrives before the frontend is updated no longer crashes the page.
   kindConfig stays exhaustive for known kinds, so TypeScript still
   catches missing entries at compile time.

Also adds src/components/ActivityFeed.test.tsx with three regression
tests (empty state, multi-item render, unknown-kind safety).

src/types/index.ts

@@ -20,7 +20,11 @@ export type ActivityKind =
   | "claim_denied"
   | "claim_accepted"
   | "remit_received"
-  | "provider_added";
+  | "provider_added"
+  // Emitted by `cyclone.store.record_manual_match` when an operator
+  // pairs a remit to a claim by hand. Surface as a neutral event on
+  // the Activity Log; do NOT treat it as a status change.
+  | "manual_match";
 
 export interface Claim {
   id: string;