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/session/session-manager.ts

@@ -1265,7 +1265,9 @@ export class SessionManager {
 		if (!this.persist || !this.sessionFile) return;
 		await this._queuePersistTask(async () => {
 			await this._closePersistWriterInternal();
-			const entries = await Promise.all(this.fileEntries.map(entry => prepareEntryForPersistence(entry, this.blobStore)));
+			const entries = await Promise.all(
+				this.fileEntries.map(entry => prepareEntryForPersistence(entry, this.blobStore)),
+			);
 			await this._writeEntriesAtomically(entries);
 			this.flushed = true;
 		});