fix(components): flatten desktop sidebar, side panel, and terminal dock chrome

[zxch3n]

Risk: 🟢 low | Confidence: high — visual chrome only; collapse/resize geometry updated with the inset removal. No schema or protocol change.

Summary

• Left nav, right side panel, and terminal dock no longer float as inset cards. They are full-bleed with a hairline (border-r / border-l / border-t).
• Drop the extra top/bottom/left margins, rounded corners, and drop shadows.
• Collapse slide, resize sash, and macOS traffic-light toggle geometry follow the flush edges.
• Active tab pills keep fill + border, lose the panel shadow.
• Tour and landing preview match the new chrome.

Test plan

• vitest terminal-dock.test.tsx
• Electron: traffic lights vs collapse/expand at 23px centerline
• Collapse the sidebar — no leftover border; sash hover sits on the divider
• Right panel and terminal dock flush with the window, no floating gutter