fix(android): improve Termux compatibility

[yan-ad]

Summary

• allow Android builds without the desktop-only clipboard dependency
• use Termux:API storage picker for image attachments on Android
• stop stale tool state from keeping the TUI redraw loop active after chat activity
• make remote client scripts work with npm as well as Bun

Notes

Image attachment on Termux requires the Termux:API app and termux-api package. Android clipboard image access is not available through Termux:API, so the attachment shortcut opens the Android file picker.

Validation

• cargo fmt --check
• focused image attachment and app tests
• cargo check

Closes #51
Closes #52

[Blankeos]

lgtm. thank you!