Discoverable window-frame and chrome controls

[tamirelazar]

Adds F10 to cycle chrome style (reaching the previously CLI-only Expanded mode), surfaces the window-frame and chrome keybinds in the keyboard-hints overlay, and documents F10 in the README.

Changes

• ControlAction::CycleChrome + RuntimeState::cycle_chrome_style() — cycles chrome style Minimal → Expanded → Fullscreen and syncs base_chrome_state/chrome_state (makes the CLI-only Expanded mode reachable at runtime)
• F10 keybinding → CycleChrome, with run-loop window-layout sync mirroring the existing F11 fullscreen handling
• Window-frame (( / )) and chrome (F10) rows added to the keyboard-hints (?) overlay
• README Appearance controls table documents F10

Test plan

• cargo test — all green (758 lib + 46 visual regression + integration)
• cargo clippy --all-targets -- -D warnings — clean
• cargo fmt --check — clean
• Manual: F10 cycles chrome, notification shows current style, keyboard-hints (?) overlay lists both controls