feat(coding-agent): added cursor navigation to message boundaries

- Added `moveCursorToMessageStart()` and `moveCursorToMessageEnd()` prompt actions for cursor navigation to message boundaries.
- Exposed editor methods for cursor movement to message start and end positions in InputController keybindings.
- Implemented message boundary navigation in Editor class with private helper methods for cursor positioning.
- Removed remote compaction settings test suite to align with feature deprecation.

packages/coding-agent/src/modes/controllers/input-controller.ts

@@ -535,6 +535,8 @@ export class InputController {
 			keybindings: this.ctx.keybindings,
 			copyCurrentLine: () => this.handleCopyCurrentLine(),
 			copyPrompt: () => this.handleCopyPrompt(),
+			moveCursorToMessageEnd: () => this.ctx.editor.moveToMessageEnd(),
+			moveCursorToMessageStart: () => this.ctx.editor.moveToMessageStart(),
 			moveCursorToLineStart: () => this.ctx.editor.moveToLineStart(),
 			moveCursorToLineEnd: () => this.ctx.editor.moveToLineEnd(),
 		});