chrome: greatly improve soft-keyboard visibility & layout handling

This reworks how we detect and respond to the on-screen keyboard so inputs
don’t get buried and the UI doesn’t “jump”.

- Add SoftKeyboardAnim + AnimState FSM for smooth IME open/close animation
- Centralize logic in keyboard_visibility() with clear edge states
- Animate keyboard height via animate_value_with_time instead of layer
  transforms
- Add ChromeOptions::KeyboardVisibility flag when focused input would be
  occluded
- Add SidebarOptions::Compact to collapse sidebar while typing
- Hide mobile toolbar when keyboard is open (columns app)
- Use .stick_to_bottom(true) in reply + profile editors; remove old spacer hack
- Virtual keyboard toggle moved to F1 in Debug builds
- Introduce SoftKeyboardContext::platform(ctx) helper
- Cleanup dead/commented code and wire up soft_kb_anim_state in Chrome

Result: inputs stay visible, open/close is smooth, and UI adjusts gracefully
when typing.

Signed-off-by: William Casarin <jb55@jb55.com>

crates/notedeck_chrome/src/options.rs

@@ -20,6 +20,9 @@ bitflags! {
 
         /// Repaint debug
         const RepaintDebug = 1 << 3;
+
+        /// We need soft keyboard visibility
+        const KeyboardVisibility = 1 << 4;
     }
 }