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_columns/src/ui/note/reply.rs

@@ -55,6 +55,7 @@ impl<'a, 'd> PostReplyView<'a, 'd> {
     pub fn show(&mut self, ui: &mut egui::Ui) -> PostResponse {
         ScrollArea::vertical()
             .id_salt(self.scroll_id)
+            .stick_to_bottom(true)
             .show(ui, |ui| self.show_internal(ui))
             .inner
     }
@@ -121,7 +122,7 @@ impl<'a, 'd> PostReplyView<'a, 'd> {
             // large and things start breaking. I think this is an ok
             // solution but there could be a better one.
             //
-            ui.add_space(500.0);
+            //ui.add_space(500.0);
 
             post_response
         })

crates/notedeck_columns/src/ui/profile/edit.rs

@@ -37,6 +37,7 @@ impl<'a> EditProfileView<'a> {
     pub fn ui(&mut self, ui: &mut egui::Ui) -> bool {
         ScrollArea::vertical()
             .id_salt(EditProfileView::scroll_id())
+            .stick_to_bottom(true)
             .show(ui, |ui| {
                 banner(ui, self.state.banner(), 188.0);