feat(tui): removed cursor positioning and refactored TUI rendering with explicit env defaults

- Removed getCursorPosition() method from Component interface and implementations, eliminating hardware cursor positioning support.
- Changed PI_HARDWARE_CURSOR environment variable default from implicit true to explicit '1' with fallback pattern.
- Changed PI_CLEAR_ON_SHRINK environment variable default from implicit false to explicit '0' with fallback pattern.
- Added screen clearing on TUI startup to prevent shell prompts from bleeding into first rendered frame.
- Refactored full-render logic into reusable fullRender() helper function.

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

@@ -84,7 +84,7 @@ export class SelectorController {
 						},
 						getStatusLinePreview: () => {
 							// Return the rendered status line for inline preview
-							const width = this.ctx.ui.getWidth();
+							const width = this.ctx.ui.terminal.columns;
 							return this.ctx.statusLine.getTopBorder(width).content;
 						},
 						onPluginsChanged: () => {