feat(lock): main-window lock screen; harden env gating, sandbox and ssh teardown

Lock screen (main-window overlay, no second window):
- scrypt password verifier in <userData>/lock.json (per-write salt,
  timingSafeEqual); salt/hash/password never leave the main process
- lock now / idle auto-lock / lock at startup, growing failure cooldown,
  lock flags persisted so a quit-and-relaunch cannot bypass the lock
- locked shell and body portals go inert while sessions keep running;
  menu accelerators (reload, DevTools, zoom) are swallowed while locked
- settings gains a Lock tab; all copy in zh-CN/zh-TW/en/ja

Security and stability:
- packaged builds ignore ELECTRON_RENDERER_URL / OT_UPDATE_URL (devEnv)
- renderer preload runs with sandbox: true
- unreadable known_hosts store fails closed instead of being overwritten
- connect-time secrets gated by the bookmark's auth method (connectPromptFor)
- ssh stream teardown is idempotent: PTY_EXIT broadcasts exactly once
- sysinfo polling is refcounted for split panes (forceStopPolling on close)
- session-log index entries are path-contained; settings store writes
  atomically with EPERM/EBUSY retry
- sync-changelog tolerates CRLF checkouts (was a silent no-op)
- retry ssh2 host-key generation (flaky malformed key, ~1/500)

Tests: lock-store + lock-controller suites; transport-death PTY_EXIT e2e;
GitHub Actions CI (typecheck + 10 offline tests + build)

tests/ssh-loopback.mjs

@@ -25,7 +25,22 @@ const fail = (msg) => {
 }
 
 // ---- 1. Boot the loopback server -------------------------------------------
-const serverKey = utils.generateKeyPairSync('ed25519')
+// ssh2's ed25519 keygen turns out a malformed key roughly once per few
+// hundred runs — its own parser then rejects it ("Malformed OpenSSH private
+// key"), which is enough to flake a release build's pretest. The Server
+// constructor parses hostKeys eagerly, so generate until one is accepted.
+function newHostKey() {
+  for (let attempt = 0; ; attempt++) {
+    const pair = utils.generateKeyPairSync('ed25519')
+    try {
+      new Server({ hostKeys: [pair.private] }, () => {})
+      return pair
+    } catch (err) {
+      if (attempt >= 9) throw err
+    }
+  }
+}
+const serverKey = newHostKey()
 let serverPort = 0
 let seenWindowChange = { cols: 0, rows: 0 }