chore(dev): give dev builds their own userData and single-instance lock

A dev instance shared the installed build's userData directory and lock, so
starting it demanded killing the real app and it wrote test settings and
session snapshots into the live profile. Dev now uses OpenTerminal-dev and
tags its window title '(dev)'; both instances run side by side.

src/main/index.ts

@@ -20,6 +20,15 @@ function showOrCreate(): void {
   }
 }
 
+// Dev runs get their own userData directory (settings, session snapshot,
+// command history, logs) *and* their own single-instance lock — both are keyed
+// on that path. Without this a dev instance fights the installed build: it
+// takes the lock, so the other side is refused / must be killed, and it writes
+// test data straight into the real profile. Must run before the lock below.
+if (!app.isPackaged) {
+  app.setPath('userData', join(app.getPath('appData'), 'OpenTerminal-dev'))
+}
+
 // Single instance: a second launch just surfaces the existing window (pulls
 // it out of the tray if hidden there) instead of starting another process.
 const gotSingleInstanceLock = app.requestSingleInstanceLock()
@@ -64,6 +73,15 @@ function createWindow(): void {
 
   win.on('ready-to-show', () => win.show())
 
+  // Dev window wears a "(dev)" tag so it is never confused with the installed
+  // build sitting next to it (they no longer share userData — see above).
+  if (!app.isPackaged) {
+    win.on('page-title-updated', (e) => {
+      e.preventDefault()
+      win.setTitle('OpenTerminal (dev)')
+    })
+  }
+
   // Close button → tray / exit per the closeAction setting (ask by default).
   win.on('close', (e) => {
     void onMainWindowClose(win, e, showOrCreate)