v3: wire Agent view (/agent) to real backend

[thinmintdev]

Context

v3 Phase B1 deferred Agent backend wiring. Agent view currently renders correctly from HAL0_DATA mock.

What to build

• ui/src/api/hooks/useAgent.ts — TanStack hooks for /api/agents, /api/agent/approvals, install/uninstall/approve/deny mutations + SSE /api/agent/approvals/events
• Wire Agent tabs + NoBundledAgentCard + PersonaEditModal
• AgentApprovalBell in chrome reads real approval count

Acceptance

• Inbox reads real pending approvals; SSE pushes live
• Install Hermes calls POST /api/agents/install
• PersonaEditModal saves
• Memory reset via real endpoint
• HAL0_DATA mock works via VITE_MOCK_LEMONADE=1

[thinmintdev]

Sub-gaps from the v3 React triage that fold into this Agent-wiring epic: #226 (PersonaEditModal hardcoded defaults), #227 (AgentSkills hardcoded table at extras.jsx:685), #228 (Memory '2,847 records · 184 MB' inline). All survive verbatim in v3.