feat(FN-2150): add agent memory file management

- Add core helpers to list, read, and write .fusion/agent-memory/{agentId} files with strict path validation and exports
- Add dashboard API routes and client methods for agent memory file listing and single-file read/write operations
- Expand AgentDetailView memory tab with file selection, editing, save states, and inline validation feedback
- Add route/backend coverage for agent memory file endpoints and include a @gsxdsm/fusion minor changeset

packages/core/src/index.ts

@@ -463,6 +463,9 @@ export {
   readProjectMemoryFile,
   readProjectMemoryFileContent,
   writeProjectMemoryFile,
+  listAgentMemoryFiles,
+  readAgentMemoryFile,
+  writeAgentMemoryFile,
 } from "./memory-backend.js";
 
 export {