Add project summaries and workspace-filtered conversation pagination

[JAVA-LW]

Problem

The AionUi sidebar needs two-step conversation loading: first list projects, then cursor-page conversations inside each project. The existing conversation endpoint can page globally but cannot provide project summaries or filter an exact workspace.

Proposed API

• GET /api/conversation-projects
  • Return custom project workspace paths, conversation counts, and latest activity.
  • Exclude backend-managed temporary workspaces, health-check conversations, and team conversations.
  • Remain compatible with historical rows that only persist extra.workspace.
• Extend GET /api/conversations with an exact workspace filter.
  • Reuse the existing cursor and limit response contract.

Consumer

The corresponding AionUi change loads 5 conversations per project and fetches 5 more on demand.

[JAVA-LW]

Implementation PR: https://github.com/iOfficeAI/AionCore/pull/606\nFrontend companion: iOfficeAI/AionUi#3564