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/core/src/ai-engine-loader.ts

@@ -39,7 +39,7 @@ const engineReady: Promise<void> = initEngine();
  * Returns `createFnAgent` from `@fusion/engine`, or `undefined` if the engine
  * could not be loaded (typical in tests or when engine isn't installed).
  */
-export async function getKbAgent(): Promise<CreateFnAgent> {
+export async function getFnAgent(): Promise<CreateFnAgent> {
   await engineReady;
   return createFnAgent;
 }