feat(tui): run on Node 26 (one runtime), finalize copy UX, rename to ui-opentui

Ports the engine off the second JS runtime onto Node 26.3 (node:ffi) so the
repo ships a single JavaScript runtime: child_process for the gateway, vitest
for tests, an esbuild + Solid build step. Mouse selection copies the rendered
text you highlight, and the clipboard path is crash-proofed (a broken copy
pipe no longer quits the UI). Renames the engine dir ui-tui-opentui-v2/ ->
ui-opentui/ and updates the launcher/installer/Docker references.

ui-opentui/src/test/env.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, test } from 'vitest'
+
+import { envFlag } from '../logic/env.ts'
+
+describe('envFlag', () => {
+  test('recognizes truthy values regardless of case/whitespace', () => {
+    for (const v of ['1', 'true', 'yes', 'on', 'TRUE', 'Yes', ' on ']) {
+      expect(envFlag(v, false)).toBe(true)
+    }
+  })
+
+  test('recognizes falsy values regardless of case/whitespace', () => {
+    for (const v of ['0', 'false', 'no', 'off', 'FALSE', 'No', ' off ']) {
+      expect(envFlag(v, true)).toBe(false)
+    }
+  })
+
+  test('returns fallback when unset', () => {
+    expect(envFlag(undefined, true)).toBe(true)
+    expect(envFlag(undefined, false)).toBe(false)
+    expect(envFlag('', true)).toBe(true)
+    expect(envFlag('   ', false)).toBe(false)
+  })
+
+  test('returns fallback for unrecognized garbage', () => {
+    expect(envFlag('maybe', true)).toBe(true)
+    expect(envFlag('maybe', false)).toBe(false)
+    expect(envFlag('2', true)).toBe(true)
+    expect(envFlag('enabled', false)).toBe(false)
+  })
+})