feat(server-mode): spend quota per user — no new session, prompts refused once used up

An admin sets a default spend quota on the Users page and overrides it per
user (Edit user → Spend quota: default / no limit / their own), in dollars
per local day or per sliding 5 hours. Spend is the users page's own
hourlyTokenRows + calculateCost over the sessions a user owns.

Over the quota, until it opens again:
- spawnRun refuses every start/resume/home prompt with EQUOTA (429);
- a minute sweep writes each pane's AGENTHUB_QUOTA_FILE (host: data dir,
  member: handoff dir via write-as) and hook-handler.js exits 2 on
  UserPromptSubmit from that file alone (Claude Code, Codex with trusted
  hooks) — fail-open, never asks the dashboard, never for Antigravity;
- a member's omp on the shared login loses its gateway key (clientsFor);
- panes no hook can stop (Antigravity, Cursor, Codex without trusted
  hooks, omp on its own login) are ended.

GET /api/me/quota feeds a "Quota N%" chip in the status bar.
New: server/lib/user-quota.js, user_quotas table, PUT /api/users/quota-default,
PATCH /api/users/:id {quota}, docs in SERVER-MODE.md § Spend quotas.

server/openapi-extra/auth.js

@@ -19,7 +19,8 @@
  *     (Auth) — Settings → Account: the account's own profile, password and logins
  *   - GET/PUT/DELETE /api/me/avatar (Auth) — the account's own picture
  *   - POST /api/me/avatar/url (Auth) — the picture as a link, redirected to
- *   - GET/PATCH /api/users/{id} (Auth) — the Users page's Edit user form
+ *   - GET/PATCH /api/users/{id} (Auth) — the Users page's Edit user form (its `quota` too)
+ *   - PUT /api/users/quota-default, GET /api/me/quota (Auth) — spend quotas per user
  *   - GET /api/users/{id}/avatar (Auth) — one account's picture (admin/analyst)
  *   - GET /api/users/tmux, POST /api/users/{id}/tmux-restart, POST /api/users/tmux-restart-idle
  *     (Auth) — each member's own tmux server and an admin's restart of it (S3)
@@ -37,6 +38,48 @@ const tags = [
 ];
 
 const schemas = {
+  UserQuota: {
+    type: "object",
+    description:
+      "A spend quota: `limit_usd` per `period` — `day` from the local midnight of `tz_offset` (getTimezoneOffset() minutes), or `5h`, the current UTC hour and the four before it.",
+    required: ["limit_usd", "period"],
+    properties: {
+      limit_usd: { type: "number", minimum: 0, exclusiveMinimum: true },
+      period: { type: "string", enum: ["day", "5h"] },
+      tz_offset: { type: "integer", minimum: -840, maximum: 840 },
+      source: { type: "string", enum: ["default", "user"], readOnly: true },
+    },
+  },
+  UserQuotaSetting: {
+    type: "object",
+    description:
+      "A user's own quota setting: `default` (the default applies), `unlimited`, or `custom` with its own limit.",
+    required: ["mode"],
+    properties: {
+      mode: { type: "string", enum: ["default", "unlimited", "custom"] },
+      limit_usd: { type: "number" },
+      period: { type: "string", enum: ["day", "5h"] },
+      tz_offset: { type: "integer" },
+    },
+  },
+  UserQuotaStatus: {
+    allOf: [
+      { $ref: "#/components/schemas/UserQuota" },
+      {
+        type: "object",
+        properties: {
+          spend: { type: "number", description: "USD spent in the current window" },
+          pct: { type: "number" },
+          exceeded: {
+            type: "boolean",
+            description: "Used up: new panes are refused (EQUOTA) and prompts refused by the hooks",
+          },
+          resetsAt: { type: "string", nullable: true, description: "When it opens again" },
+          since: { type: "string", description: "Start of the current window" },
+        },
+      },
+    ],
+  },
   AccountPin: {
     type: "object",
     required: ["userId", "username", "account"],
@@ -214,6 +257,32 @@ const paths = {
       },
     },
   },
+  "/api/me/quota": {
+    get: {
+      tags: ["Auth"],
+      operationId: "getMyQuota",
+      summary: "The account's own spend quota now (null without one, and in local mode)",
+      responses: {
+        200: {
+          description: "Quota",
+          content: {
+            "application/json": {
+              schema: {
+                type: "object",
+                properties: {
+                  quota: {
+                    allOf: [{ $ref: "#/components/schemas/UserQuotaStatus" }],
+                    nullable: true,
+                  },
+                },
+              },
+            },
+          },
+        },
+        401: err("EAUTH"),
+      },
+    },
+  },
   "/api/me/instructions": {
     get: {
       tags: ["Auth"],
@@ -504,11 +573,20 @@ const paths = {
                               type: "object",
                               properties: { cost: { type: "number" }, tokens: { type: "integer" } },
                             },
+                            quotaSetting: { $ref: "#/components/schemas/UserQuotaSetting" },
+                            quota: {
+                              allOf: [{ $ref: "#/components/schemas/UserQuotaStatus" }],
+                              nullable: true,
+                            },
                           },
                         },
                       ],
                     },
                   },
+                  quotaDefault: {
+                    allOf: [{ $ref: "#/components/schemas/UserQuota" }],
+                    nullable: true,
+                  },
                 },
               },
             },
@@ -712,10 +790,11 @@ const paths = {
         addWorkspaces: { type: "array", items: { type: "integer" } },
         removeWorkspaces: { type: "array", items: { type: "integer" } },
         signOut: { type: "boolean", enum: [true] },
+        quota: { $ref: "#/components/schemas/UserQuotaSetting" },
       }),
       responses: {
         ...changeResponses,
-        400: err("EBADPASSWORD / EBADROLE / EBADFIELD / EBADEMAIL"),
+        400: err("EBADPASSWORD / EBADROLE / EBADFIELD / EBADEMAIL / EBADQUOTA"),
         409: err("ESELF / ENOTOWNED / EOWNERFOLDER"),
       },
     },
@@ -734,6 +813,44 @@ const paths = {
       },
     },
   },
+  "/api/users/quota-default": {
+    put: {
+      tags: ["Auth"],
+      operationId: "setDefaultUserQuota",
+      summary:
+        "Admin: the default spend quota for every user without one of their own (`quota: null` removes it). A user over their quota can start no pane (429 EQUOTA) and their Claude Code/Codex prompts are refused by the hooks",
+      requestBody: changeBody(
+        {
+          quota: {
+            allOf: [{ $ref: "#/components/schemas/UserQuota" }],
+            nullable: true,
+          },
+        },
+        ["quota"]
+      ),
+      responses: {
+        ...changeResponses,
+        200: {
+          description: "Saved",
+          content: {
+            "application/json": {
+              schema: {
+                type: "object",
+                properties: {
+                  user: { $ref: "#/components/schemas/AuthUser" },
+                  quotaDefault: {
+                    allOf: [{ $ref: "#/components/schemas/UserQuota" }],
+                    nullable: true,
+                  },
+                },
+              },
+            },
+          },
+        },
+        400: err("EBADQUOTA"),
+      },
+    },
+  },
   "/api/users/{id}/password": {
     post: {
       tags: ["Auth"],