Desktop UX improvements: disconnect confirm, chat-first home, setup walkthrough, apps onboarding

[kotevcode]

Summary

A batch of desktop UX improvements focused on first-run experience and day-to-day polish.

Connection & status

• The Home power button asks for confirmation before disconnecting (reusable modal, "Don't show this again" checkbox).
• Power/status only show "Running" once the proxy port actually answers (1s startup probe); footer shows "Offline"/red "Stopped" instead of stale "Healthy" when routing is off.
• Floating window's "Show on traffic" preference now defaults to on.
• App-wide modal chrome restyle (borderless close button, tighter header).

Home screen

• Chat-first hero: composer card with inline model pill and square send button, placeholder "How can I help you today?".
• App pills ("Use AntSeed on your favorite app") stay visible after connecting a tool — they only disappear once chats exist; connected apps show as connected (green dot) and open the Apps page.
• Usage tiles always visible (zeros included) and always at the bottom on both variants.
• Chat view opens wide by default.

Setup screen

• Hard-coded animated walkthrough: miniature app window cycling Home → Chat → Models → Apps scenes with captions, labs marquee, and small live counts ("Setting up — only on first run, takes 2 minutes max").

Apps onboarding

• Notification dot on the Apps nav item until the screen is first opened.
• First visit plays a coach-mark tooltip over the live view with a looping mini-demo (Claude/Cursor window chatting via the VPR). Once per install.

Fixes

• T3 Code installed under any release channel (stable/Alpha/Beta/Nightly) now resolves a default app, its real icon, and restart support; official icon as fallback.
• Help view: internet-accessible endpoint row moved to the end of the VPR card.

Testing

• pnpm run test in apps/desktop (main-process tests + 350 renderer tests) and pnpm run typecheck:renderer pass; renderer build clean.
• Manually exercised on macOS dev: disconnect confirm, startup status probe, walkthrough, setup animation, T3 Code (Nightly) resolution.

CHANGELOG.md updated for all user-facing changes.