refactor(FN-2162): rename kb-agent identifiers to fn-agent

- Rename core loader, dashboard server chat/planning routes, and frontend agent IDs/storage keys from kb-agent to fn-agent naming
- Update dashboard hooks and components (agent list, chat view, quick chat) to use the new fn agent key prefixes consistently
- Refresh engine, dashboard, core, and CLI tests/mocks to remove remaining kb-agent route and temp prefix references
- Update storage/gap-analysis docs to reflect fn agent key names and add a @gsxdsm/fusion patch changeset for the rename

packages/dashboard/src/chat.ts

@@ -794,7 +794,7 @@ export class ChatManager {
 /**
  * Inject a mock createFnAgent function. Used for testing only.
  */
-export function __setCreateKbAgent(mock: typeof createFnAgent): void {
+export function __setCreateFnAgent(mock: typeof createFnAgent): void {
   createFnAgent = mock;
 }