Customize display and add chat orchestration

[chasmlol]

What changed

• remove the T3 Code stage branding and decorative sidebar header treatment
• add display settings for font scaling, text/background/accent colors, and Codex/Claude presets
• add first-class chat_* MCP tools so T3 chats can spawn, inspect, prompt, wait for, and manage other T3 chats
• queue prompts while a chat is generating, with controls to steer immediately, retry, or remove them

Why

These changes make the app feel cleaner and more personal while bringing T3 chats closer to the orchestration workflow available with subagents. Prompt queueing also prevents follow-up messages from steering an active generation by default.

User impact

Users can customize the app's appearance, manage persistent visible chats through MCP tools, and safely queue follow-up prompts without interrupting the current response.

Validation

• commit hooks ran vp fmt on every changed file
• targeted vp lint --report-unused-disable-directives passed
• contracts, web, and server typechecks passed
• contracts and web production build passed
• integrated browser verification confirmed the Display settings route, Codex/Claude preset menu, immediate font/color application, and persistence after reload
• focused test files were attempted, but the repository's current Vite+/Vitest collection issue prevented all selected suites from collecting (Cannot read properties of undefined (reading 'config') / Vitest failed to find the current suite); no test body failures occurred