UI labels (status, headings, control text) no longer selectable.
Console/hex content remains selectable for copy. ScrollArea now
nudges when drag-selecting near the bottom edge (~240px/s).
Extract types (models.rs), font settings, session controls, and send
panel into separate modules. Reduces app.rs from 1488 to 848 lines.
Zero behavior change.
- models.rs: ConnectionStatus, View, SendMode, LineEnding,
DisplayOptions, SearchState, SessionTab
- panels/font_settings.rs: font selector and settings window
- panels/session_controls.rs: session connect/disconnect UI
- panels/send_panel.rs: send input and payload building
