fix(desktop): crash on dialog open — undefined.trim()

[vanducng]

Summary

• Desktop form dialogs (MCP, Agent, Team Settings) crash with undefined is not an object (evaluating 'l("name").trim') when opened
• Root cause: useForm() called without defaultValues — watch() returns undefined on first render before useEffect fires reset()
• Fix: add defaultValues to useForm() in all 3 affected dialogs

Files Changed

• ui/desktop/frontend/src/components/mcp/McpFormDialog.tsx
• ui/desktop/frontend/src/components/agents/AgentFormDialog.tsx
• ui/desktop/frontend/src/components/teams/TeamSettingsModal.tsx

Closes #732, closes #735

Test Plan

• Open desktop app → Settings → MCP → Add MCP Server → form renders without crash
• Open desktop app → Agents → "+" button → form renders without crash
• Open desktop app → Teams → settings on any team → modal renders without crash
• Fill and submit all 3 forms — verify data saves correctly