fix(tui): termux-gate scrollback preservation, touch-friendly defaults

Adds a Termux runtime detection helper and gates three TUI defaults on it:

- Skip the startup scrollback clear on Termux so users can review/copy
  earlier output after reopening the app. Desktop keeps the existing
  \x1b[2J\x1b[H\x1b[3J slate (AlternateScreen takes over there anyway).
- Default INLINE_MODE on under Termux: primary-buffer rendering makes
  long-thread review and copy/paste much less fragile when users
  background/foreground the app. Override with HERMES_TUI_INLINE=0/1.
- Default mouse tracking off under Termux so touch selection isn't
  intercepted by terminal mouse protocols. Explicit override via
  HERMES_TUI_MOUSE_TRACKING=0/1; legacy HERMES_TUI_DISABLE_MOUSE still
  works on desktop.

Detection is purely env-based (TERMUX_VERSION or PREFIX path) with an
explicit opt-out HERMES_TUI_TERMUX_MODE=0 for debugging. Non-Termux
platforms keep every existing default.

Co-authored-by: adybag14-cyber <252811164+adybag14-cyber@users.noreply.github.com>

ui-tui/src/entry.tsx

@@ -5,6 +5,7 @@ import './lib/forceTruecolor.js'
 
 import type { FrameEvent } from '@hermes/ink'
 
+import { TERMUX_TUI_MODE } from './config/env.js'
 import { GatewayClient } from './gatewayClient.js'
 import { setupGracefulExit } from './lib/gracefulExit.js'
 import { formatBytes, type HeapDumpResult, performHeapDump } from './lib/memory.js'
@@ -21,11 +22,14 @@ if (!process.stdin.isTTY) {
 // terminal tab can still have mouse/focus/paste modes enabled.
 resetTerminalModes()
 
-// Clear visible screen + scrollback buffer. Without this, tmux may retain
-// stale TUI output in its scrollback buffer from the previous session,
-// which is visible when the user scrolls up or briefly before AlternateScreen
-// takes over on restart. See entry.tsx → AlternateScreen flow.
-process.stdout.write('\x1b[2J\x1b[H\x1b[3J')
+// Desktop terminals benefit from a clean startup slate because the TUI usually
+// runs in AlternateScreen. On Termux we keep prior output intact so users can
+// review/copy earlier assistant replies after reopening the app.
+if (TERMUX_TUI_MODE) {
+  process.stdout.write('\n')
+} else {
+  process.stdout.write('\x1b[2J\x1b[H\x1b[3J')
+}
 
 const gw = new GatewayClient()