Drag panes onto tabs to move them or break them into a new tab

[Hon-Lu]

Summary

• Dragging a pane's handle onto another tab moves the pane into that tab; dropping on + breaks it out into a new tab
• Holding over a tab opens it, then dropping on a pane edge places the pane on that side (left/up use move + swap, since Herdr only splits right/down)
• Same-tab drops still swap; a pinned tab's last pane cannot be moved out
• Uses Herdr's native pane.move, so running processes keep going
• Raises the initial JS budget from 802 to 804 KiB

Known limitation: tabs scrolled out of the strip (and + when pushed off-screen) can't be reached while dragging. See #439.

Verification
bun run lint, bun run typecheck, bun run build:web, related bun test files; manually tested against Herdr 0.9.3 in Chrome.