Memory page node selector: show node titles instead of node IDs

[rowan-stein]

User request

Memory page has a memory node selector that currently displays node IDs. Change it to display node titles.

Specification (research)

Current behavior / locations

• Memory node selector labels are built in packages/platform-ui/src/pages/AgentsMemoryManager.tsx and shown in dropdown in packages/platform-ui/src/components/screens/memoryManager/MemoryManager.tsx.
• Labels are currently based on nodeId (e.g., "{nodeId} (global)", "{nodeId} (thread: ...)").

Where titles come from

• Memory API items include nodeId, scope, and optional threadId, but do not include title.
• Node titles can be derived from the Graph + Templates APIs:
  • /api/graph (persisted graph)
  • /api/graph/templates (template metadata)
  • Existing mapper packages/platform-ui/src/features/graph/mappers/index.ts (mapPersistedGraphToNodes) derives node.title from config/template.

Implementation approach

• Add a shared client hook (suggested): useNodeTitleMap() that fetches graph + templates (via existing graph api module) and returns a Map<nodeId, title>.
• Update UI to use title (fallback to nodeId if not resolvable):
  1. packages/platform-ui/src/pages/AgentsMemoryManager.tsx
     • Update option label builder to use titleMap.get(nodeId) ?? nodeId.
  2. (Optional but recommended for consistency) packages/platform-ui/src/pages/MemoryNodesListPage.tsx and packages/platform-ui/src/pages/MemoryNodeDetailPage.tsx
     • Replace prominent nodeId display with title, with fallback.

Acceptance criteria

• Memory node selector shows node titles (derived from graph/templates) instead of raw node IDs.
• If a title cannot be resolved (loading/error/stale node), UI falls back to showing the node ID.
• Existing selection behavior remains unchanged (still keyed by nodeId).