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/components/diff.ts

@@ -1,5 +1,6 @@
 import * as Diff from "diff";
 import { theme } from "../../modes/theme/theme";
+import { replaceTabs } from "../../tools/render-utils";
 
 /**
  * Parse diff line to extract prefix, line number, and content.
@@ -11,13 +12,6 @@ function parseDiffLine(line: string): { prefix: string; lineNum: string; content
 	return { prefix: match[1], lineNum: match[2] ?? "", content: match[3] };
 }
 
-/**
- * Replace tabs with spaces for consistent rendering.
- */
-function replaceTabs(text: string): string {
-	return text.replace(/\t/g, "   ");
-}
-
 /**
  * Compute word-level diff and render with inverse on changed parts.
  * Uses diffWords which groups whitespace with adjacent words for cleaner highlighting.