[florent37]

Description

Replaces the accessibility focus bar of the desktop app with a floating TalkBack remote, and adds an "activate" action (the TalkBack double tap).

Desktop

• New AccessibilityRemote: a card that floats over the Accessibility screen. It shows the focused element (class, title, bounds, position) and has these buttons:
  • previous / OK / next
  • "Get focused element"
• The remote can be dragged by its handle and stays inside the screen. It starts at the bottom end and can collapse into a bubble. The position and collapsed state are UI state only.
• New ActivateAccessibilityFocusedNodeUseCase, wired through the repository and the to-device data source.
• The event list now takes the full height (the old AccessibilityFocusedNodeCard is removed).

Protocol / SDK

• New Desktop → Mobile method Activate in both Protocol.kt, documented in protocol/accessibility.md.
• Android: clicks the element that has the accessibility focus (ACTION_CLICK on a View, or through the Compose accessibility node provider), then replies with FocusedNode. Other platforms reply with an empty FocusedNode.
• Backward compatible: an older SDK ignores the unknown method.

Checks

• :accessibility:jvmTest, :accessibility-no-op:compileKotlinJvm, :accessibility:compileAndroidMain
• :composeApp:compileKotlinDesktop, :domain:allTests, :data:core:allTests, :mcp:allTests, ktlintCheck
• Not checked at runtime: dragging, collapsing and the click on a real device.

/gemini review