D-23: MainFeature — view routing by tab.surface

[kirich1409]

Description

Update MainFeature view layer to render either TerminalView or DialogueView based on the currently selected tab's surface.

Spec: Epic #250 §5.

Scope

File

MacApp/Relay/MainFeature.swift or the corresponding view file.

Switch

```swift
switch selectedTab.surface {
case .shell, .agentTerminal:
TerminalView(store: store.scope(state: .currentTerminalFeature, action: .terminal))
case .agentDialogue:
DialogueView(store: store.scope(state: .currentDialogueFeature, action: .dialogue))
}
```

Ensure scoping maps to the active tab's AgentSessionFeature.State.presentation case.

Empty states

• No tabs → Welcome screen (unchanged).
• Tab with no started session → placeholder.

Acceptance Criteria

• View routes correctly: .shell / .agentTerminal → TerminalView; .agentDialogue → DialogueView.
• Switching between tabs of different surfaces updates view instantly.
• Per-window environment injection for DesignSystem (.designSystem(...)) applied to DialogueView the same way as to TerminalView.

Relationships

• Parent issue: EPIC: Dialogue — structured chat UI for agent sessions #250
• Blocked by: #D-18, #D-21, #D-22
• Blocks: #D-27 (a11y sweep of the whole integrated app)