feat: polish mobile sessions and reconnect flow

[wisdomqin]

Summary

• refine the mobile session list and conversation layout, including the compact overlay composer, native back navigation, reduced reconnect-page hierarchy, and automatic light/dark appearance
• let Home Screen installs reconnect after desktop disconnection, retry expired approval requests, reopen desktop approval automatically, and restore the existing mobile context after approval
• anchor the desktop phone action directly to the settings row so footer plugins such as usage and billing cards cannot shift its position
• replace the desktop startup loader with the updated transparent whale animation and soften the desktop approval request accent
• stamp Windows advanced-titlebar environment parameters so compatible plugins such as Better Sidebar can avoid native window controls

Verification

• npm test — 25 test files, 156 tests passed
• npm run typecheck
• manually verified the mobile reconnect and approval retry flow against the running development app

Related

• Better Sidebar dynamic Window Controls Overlay follow-up: [Windows/Desktop] 使用 Window Controls Overlay 实际几何动态避让原生按钮 omdsh-dev/DSH-better-sidebar#257