Background

Currently Agent and Assistant are mixed in the same list (UnifiedList). Users report difficulty finding the Agent entry. The two have significant differences in functionality, data models, and interaction patterns:

Issues caused by mixing:

1. Users cannot intuitively find the Agent entry, low discoverability
2. Two fundamentally different models forced to share list and tab switching logic
3. Selecting an Agent requires setting a fake assistant (id: 'fake') to work around null issues

Goal

Complete separation of Agent and Assistant:

• Assistant page (/): Only shows assistant list + Topics + assistant chat
• Agent page (/agents): Only shows Agent list + Sessions + Agent chat
• Both sides are independent with their own data and UI
• Agent has a fixed tab in the top navigation bar next to "首页" for quick access

Design

1. Add: Sidebar Agent entry + Route + Page

Add agents entry to sidebar using MousePointerClick icon (lucide-react), navigates to /agents.

Sidebar:
┌──────┐
│ 💬   │ ← assistants (assistants only)
│ 🖱️   │ ← agents (agents only)
│ 🏪   │ ← store
│ ...  │
└──────┘

Agent page structure is identical to the current experience when selecting an Agent in HomePage:

• Left panel: Agent list + Session list (reuse existing display logic)
• Right panel: <Chat /> (internally activeTopicOrSession === 'session' auto-renders AgentSessionMessages + AgentSessionInputbar)
• Add button: directly creates a new Agent

2. Add: Fixed Agent tab in top navigation bar (tab-style)

In the top content area header (NavbarCenter), add a tab-style navigation bar with "首页" (Home) and "Agent" as fixed tabs, along with a "+" button.

┌────────────────────────────────────────────────────────────────┐
│  ☰  📋    [ 首页 ] [ 🖱️ Agent ] [ + ]          🔍   ↔   📋  │
│  NavbarLeft          NavbarCenter               NavbarRight   │
└────────────────────────────────────────────────────────────────┘

• 首页 tab: Represents the current Assistant/Home page (/), highlighted when on home page
• Agent tab: Fixed tab, clicking navigates to /agents, highlighted when on Agent page
• + button: Context-aware — on home page creates new assistant, on Agent page creates new Agent
• Tab style: Matches existing tab styling patterns in the app (active underline indicator, font weight change)
• Both tabs are always visible regardless of current route

3. Cleanup: Remove Agent from Assistant page

Assistant list no longer shows Agents. HomePage no longer handles Agent logic.

4. Unchanged files

Change Summary

Future Work (not in this PR)

• Clean up deprecated Agent state management in runtime.ts (v2 refactor)