feat(frontend): UI for affinity_mode + per-key limits

Settings page (#150 backend):
- New "Session affinity" select with bounded / off / strict options.
  Defaults to bounded; loaded from /api/admin/settings.

API Keys page (#146 backend):
- New collapsible "Advanced limits" section in both create and edit
  modals, auto-expanded when any limit is configured.
- Model allowlist/denylist via ChipInput, sourced from current
  /api/admin/models so users can pick existing model IDs but also
  type custom ones.
- Six numeric fields: rpm, rpd, cost_limit_5h/7d, token_limit_5h/7d
  with appropriate suffix labels ($, tk, /min, /day) and step.
- limitsFromAPIKey / limitsFormToPayload bridge between
  APIKeyLimits (snake_case backend type) and the form state.
- types.ts: APIKeyLimits + APIKeyRow.limits.

Verified end-to-end against 2004 instance.

Author: james-6-23

frontend/src/locales/en.json

@@ -998,6 +998,11 @@
     "schedulerModeDesc": "Round Robin distributes requests evenly across accounts. Remaining Quota prefers accounts with lower usage percentage.",
     "schedulerModeRoundRobin": "Round Robin",
     "schedulerModeRemainingQuota": "Remaining Quota",
+    "affinityMode": "Session Affinity",
+    "affinityModeDesc": "Bounded (default): same session sticks to one account but auto-rotates after 50 requests, 5 minutes, or when the bound account becomes unhealthy. Off: every request re-picks via scheduler. Strict: legacy behavior, sticks long-term.",
+    "affinityModeBounded": "Bounded (recommended)",
+    "affinityModeOff": "Off (re-pick every request)",
+    "affinityModeStrict": "Strict (long-term sticky)",
     "allowRemoteMigration": "Allow Remote Migration",
     "allowRemoteMigrationDesc": "When enabled, other codex2api instances can pull healthy accounts from this instance.",
     "allowRemoteMigrationRequiresSecret": "Set an admin secret first. Remote migration cannot be enabled without admin authentication.",
@@ -1250,6 +1255,27 @@
     "hideKey": "Hide key",
     "allowedGroups": "Allowed Groups",
     "allowedGroupsHint": "Leaving this empty allows the key to use all account groups.",
+    "limits": {
+      "title": "Advanced limits",
+      "active": "active",
+      "show": "Expand",
+      "hide": "Collapse",
+      "desc": "Apply per-key model scope and sliding-window quota. Leave a field empty to skip it.",
+      "modelAllow": "Model allowlist",
+      "modelAllowPlaceholder": "Pick or type a model, press Enter",
+      "modelAllowHint": "When non-empty, only listed models are allowed; otherwise the denylist applies.",
+      "modelDeny": "Model denylist",
+      "modelDenyPlaceholder": "Pick or type a model to deny",
+      "modelDenyHint": "Used only when the allowlist is empty.",
+      "rpm": "Requests per minute",
+      "rpmSuffix": "/min",
+      "rpd": "Requests per day",
+      "rpdSuffix": "/day",
+      "cost5h": "Cost limit (5h)",
+      "cost7d": "Cost limit (7d)",
+      "tokens5h": "Token limit (5h)",
+      "tokens7d": "Token limit (7d)"
+    },
     "allowedGroupsLabel": "Allowed Account Groups",
     "allowedGroupsPlaceholder": "Choose allowed groups",
     "allowedGroupsAll": "All groups",

frontend/src/locales/zh.json

@@ -998,6 +998,11 @@
     "schedulerModeDesc": "轮询模式在所有账号间平均分配请求。剩余配额模式优先使用用量较低的账号。",
     "schedulerModeRoundRobin": "轮询",
     "schedulerModeRemainingQuota": "剩余配额",
+    "affinityMode": "会话粘性",
+    "affinityModeDesc": "Bounded（默认）：同一会话粘到同一账号,但累计 50 次请求或绑定 5 分钟后自动换号,绑定账号变为非健康也会换号。Off：每次请求都按调度模式重新挑号,严格分散。Strict：旧行为,长期粘到底。",
+    "affinityModeBounded": "Bounded（推荐）",
+    "affinityModeOff": "关闭（每次重新挑号）",
+    "affinityModeStrict": "Strict（长期粘连）",
     "allowRemoteMigration": "允许远程迁移",
     "allowRemoteMigrationDesc": "开启后，其他 codex2api 实例可通过导出接口拉取本实例的健康账号。",
     "allowRemoteMigrationRequiresSecret": "请先设置管理密钥，未设置密码时不能启用远程迁移。",
@@ -1250,6 +1255,27 @@
     "hideKey": "隐藏密钥",
     "allowedGroups": "允许分组",
     "allowedGroupsHint": "不选择表示该密钥可使用全部账号分组。",
+    "limits": {
+      "title": "高级限制",
+      "active": "已启用",
+      "show": "展开",
+      "hide": "收起",
+      "desc": "对该密钥单独施加模型范围与时间窗口配额。空字段表示不限。",
+      "modelAllow": "模型白名单",
+      "modelAllowPlaceholder": "选择或输入模型名,Enter 添加",
+      "modelAllowHint": "白名单非空时,只允许调用其中的模型;为空则使用黑名单。",
+      "modelDeny": "模型黑名单",
+      "modelDenyPlaceholder": "选择或输入要拒绝的模型",
+      "modelDenyHint": "白名单为空时生效。",
+      "rpm": "每分钟请求",
+      "rpmSuffix": "/min",
+      "rpd": "每天请求",
+      "rpdSuffix": "/day",
+      "cost5h": "5h 成本上限",
+      "cost7d": "7d 成本上限",
+      "tokens5h": "5h Token 上限",
+      "tokens7d": "7d Token 上限"
+    },
     "allowedGroupsLabel": "允许账号分组",
     "allowedGroupsPlaceholder": "选择允许调用的分组",
     "allowedGroupsAll": "全部分组",