Add Server Restart settings tab to admin panel

[AdaInTheLab]

Summary

UI surface for the `GracefulRestartFeature` backend that landed in #57. Now admins can configure scheduled restarts and trigger one-off restarts from the panel without touching the REST API or console.

What's in the tab

• Master toggle: Enable Daily Restart
• Schedule: time of day (HH:mm) + IANA timezone (text input — IANA list is too long for a Select)
• Warning ladder: inline editable table with add/remove. Per row: minutes-before, message, BBGGRR color hex. Sorted descending on render so the first-firing step is on top
• Restart Now panel on the right: lead-time input + a danger-styled button with `confirm()` prompt before kicking off

Layout mirrors the Vote Rewards tab — 2-col with schedule/ladder left, trigger right. Collapses to single col under 768px.

Files

File	What
`frontend/src/api/restart.ts`	REST client (3 endpoints)
`frontend/src/types/index.ts`	`GracefulRestartSettings`, `RestartWarning`
`frontend/src/views/SettingsView.vue`	New tab (value="10") + state + handlers + CSS
`frontend/src/i18n/locales/en.ts`	Canonical strings
`frontend/src/i18n/locales/{ja,ko,zh-CN,zh-TW}.ts`	English placeholders, "translations TBD"

Test plan

• Pull, build, deploy
• Hard-refresh panel → Settings tab list shows "Server Restart" after "Vote Rewards"
• Tab loads with current backend settings (default ladder visible: 10 / 5 / 1 / 0)
• Edit a step's message → Save → reload tab → change persists
• Add a new step at 30 min → Save → confirm via `GET /api/restart/settings` it's in the JSON
• Remove a step → Save → confirm gone
• Toggle Enable on, set schedule to 12 minutes from now, Save
• Wait → countdown plays in-game → server restarts → systemd brings it back
• Click Restart Now with lead=2 → in-game broadcasts at 2/1/0 → shutdown → recover

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