Add transcript display modes and selection UI

[acgxv]

Context: Floating panel notes list deferred enhancements for transcript display modes and a settings popover.

Scope:

• Add transcript display modes: single-line (default), auto-grow capped lines, fully expanded.
• Provide a settings popover to select the display mode.

Reference: docs/guide/development/ui_floating_panel_notes.md (Deferred enhancements).

Acceptance:

• Modes are implemented and selectable.
• Defaults and behavior are documented.
• UI matches existing panel interaction patterns.