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)

src/shared/api.ts

@@ -10,6 +10,7 @@ import type {
 } from './ipc'
 import type { AppSettings } from './settings'
 import type { ReleaseNote, UpdateState } from './ipc'
+import type { LockOperationResult, LockPasswordInput, LockSettingsState } from './ipc'
 import type {
   HostKeyAction,
   HostKeyPromptEvent,
@@ -100,6 +101,17 @@ export interface AppApi {
   saveSettings(next: Partial<AppSettings>): Promise<AppSettings>
   onSettingsChanged(cb: (s: AppSettings) => void): () => void
 
+  // ---- lock screen (main-window overlay; main owns the lock state) ----
+  getLockState(): Promise<LockSettingsState>
+  /** set or replace the password; verifies currentPassword when one exists */
+  setLockPassword(input: LockPasswordInput): Promise<LockOperationResult>
+  /** remove the password; verifies currentPassword when one exists */
+  clearLockPassword(input: { currentPassword?: string }): Promise<LockOperationResult>
+  /** answer the lock screen; resets the failure cooldown on success */
+  unlockLock(input: { password?: string }): Promise<LockOperationResult>
+  lockNow(): Promise<LockSettingsState>
+  onLockStateChanged(cb: (state: LockSettingsState) => void): () => void
+
   // ---- fonts ----
   listFonts(): Promise<string[]>