fix: v2.5.9 — Vietnamese in the terminal on macOS, every slash command, the right Claude account

Issue #62: a tmux client whose LC_ALL/LC_CTYPE/LANG names no UTF-8 prints `_`
for every non-ASCII character, and a macOS LaunchAgent starts the dashboard
with no locale at all — Vietnamese text and Claude Code's logo came out as
underscores in every browser terminal.

- shell-path.js: ensureUtf8Locale() defaults LC_CTYPE (en_US.UTF-8 on macOS,
  C.UTF-8 elsewhere) at start, before any tmux call; an explicit LC_ALL and
  Windows are left alone
- RunSetup.tsx: the `/` list now offers Claude Code's bundled skills
  (/code-review, /security-review, /simplify, /loop…) and newer built-ins, and
  every enabled plugin's commands and skills as /<plugin>:<name>
- Claude login decided by the TOKEN's owner (GET /api/oauth/profile, cached
  per token), not by .claude.json: a running session can leave the
  credentials store holding one account's token under another account's
  name. The Profiles modal, its Check quota and the status-bar quota now show
  the account requests are really billed to and warn on the mismatch; a
  switch saves the outgoing token into its OWNER's profile (credentials only)
  instead of overwriting the profile .claude.json names; saving a profile
  while they disagree is refused (EMISMATCH); a saved profile holding another
  account's token reports EWRONGACCOUNT instead of that account's usage
- Running Claude Code sessions follow a switch on their own (they re-read the
  credentials store when it changes), so the "close your sessions first"
  warning is gone

client/src/i18n/locales/vi/nav.json

@@ -79,6 +79,7 @@
     "quotaRefreshing": "Đang làm mới…",
     "quotaExpired": "Token đã hết hạn: dùng Claude Code một lần để nó tự làm mới",
     "quotaFailed": "Không đọc được quota",
+    "quotaWrongAccount": "Lượt đăng nhập này thuộc tài khoản Claude khác: đăng nhập lại đúng tài khoản này rồi lưu lại",
     "quotaActive": "đang dùng",
     "quotaProfileExpired": "Đăng nhập đã hết hạn: bấm Kiểm tra quota trong Claude Code → Profiles để làm mới",
     "quotaSignInExpires": "Đăng nhập hết hạn sau {{time}}",