feat: persist quota state across restarts and add TUI account reorder

[rlawjdghksdlqslek]

Summary

Two related quality-of-life improvements for TeamClaude's account management:

1. Persist quota state across server restarts

Previously, quota counters (5h/7d unified usage, token limits, reset timestamps)
were reset to zero every time the server restarted. This made it impossible to
track remaining quota accurately after a restart.

• Adds exportQuota() to AccountManager to serialize quota fields safe for config storage
• Saves quota state to savedQuota in the config file every 60 seconds via a periodic
  interval
• Restores saved quota on startup when loading accounts
• Flushes quota state to disk on graceful shutdown (SIGINT, SIGTERM, and TUI quit)

2. TUI account reorder with o key

Adds an interactive reorder mode to the TUI so users can reorganize the account
list without manually editing the config file.

• Press o in normal mode to enter reorder mode
• Navigate with ↑/↓ (or j/k), press Enter to grab an account
• Move the grabbed account up/down, press Enter to confirm or Esc to cancel
• Saves the new order to config on confirm
• Updates currentIndex correctly when accounts are moved around

Files Changed

• src/account-manager.js — exportQuota(), moveAccount(), quota restore on init
• src/index.js — periodic quota save, flush on shutdown
• src/tui.js — reorder mode, _keyReorder(), _doSaveReorder(), footer hint update

Test Plan

• Start server, make some requests to accumulate quota usage, restart — verify quota
  values are preserved in TUI
• In TUI, press o, reorder accounts, confirm — verify new order persists after restart
• In TUI, press o, reorder, press Esc — verify order is reverted
• Verify currentIndex stays on the correct account after reordering