feat: per-account quota threshold protection (#212)

feat: per-account quota threshold protection

Resolves #135

- Adds configurable quota protection with three-tier threshold resolution (per-model → per-account → global)
- New global Minimum Quota Level slider in Settings
- Per-account threshold settings via Account Settings modal
- Draggable per-account threshold markers on model quota bars
- Backend: PATCH /api/accounts/:email endpoint, globalQuotaThreshold config
- i18n: quota protection keys for all 5 languages

public/js/translations/id.js

@@ -270,6 +270,11 @@ window.translations.id = {
     defaultCooldownDesc: "Cooldown bawaan jika API tidak memberikan waktu reset.",
     maxWaitThreshold: "Batas Tunggu Maksimal",
     maxWaitDesc: "Jika semua akun terkena rate limit lebih lama dari ini, langsung gagal.",
+    // Perlindungan Kuota
+    quotaProtection: "Perlindungan Kuota",
+    minimumQuotaLevel: "Level Kuota Minimum",
+    minimumQuotaLevelDesc: "Ganti akun ketika kuota turun di bawah level ini. Pengaturan per-akun lebih diutamakan.",
+    quotaDisabled: "Nonaktif",
     // Error Handling Tuning
     errorHandlingTuning: "Penyetelan Penanganan Error",
     rateLimitDedupWindow: "Jendela Deduplikasi Rate Limit",