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/__tests__/termux.test.ts

@@ -0,0 +1,35 @@
+import { describe, expect, it } from 'vitest'
+
+import { isTermuxEnv, isTermuxTuiMode } from '../lib/termux.js'
+
+describe('isTermuxEnv', () => {
+  it('detects TERMUX_VERSION marker', () => {
+    expect(isTermuxEnv({ TERMUX_VERSION: '0.118.0' } as NodeJS.ProcessEnv)).toBe(true)
+  })
+
+  it('detects Termux PREFIX path marker', () => {
+    expect(
+      isTermuxEnv({ PREFIX: '/data/data/com.termux/files/usr' } as NodeJS.ProcessEnv)
+    ).toBe(true)
+  })
+
+  it('returns false for generic Linux envs', () => {
+    expect(isTermuxEnv({ PREFIX: '/usr' } as NodeJS.ProcessEnv)).toBe(false)
+  })
+})
+
+describe('isTermuxTuiMode', () => {
+  it('defaults to true inside Termux', () => {
+    expect(isTermuxTuiMode({ TERMUX_VERSION: '0.118.0' } as NodeJS.ProcessEnv)).toBe(true)
+  })
+
+  it('allows explicit opt-out override', () => {
+    expect(
+      isTermuxTuiMode({ TERMUX_VERSION: '0.118.0', HERMES_TUI_TERMUX_MODE: '0' } as NodeJS.ProcessEnv)
+    ).toBe(false)
+  })
+
+  it('stays false outside Termux even if override is set', () => {
+    expect(isTermuxTuiMode({ HERMES_TUI_TERMUX_MODE: '1', PREFIX: '/usr' } as NodeJS.ProcessEnv)).toBe(false)
+  })
+})