feat(panel): let a sponsor slot start at a scheduled time

sponsors.json only had an end date, so a booked placement had to be
added to the file on the day it started. An optional `from` now hides
a sponsor (and its logo) until that instant; entries without it show
immediately as before.

frontend/src/generated/examples.ts

@@ -1107,6 +1107,7 @@ export const EXAMPLES: Record<string, unknown> = {
   },
   "Sponsor": {
     "enable": true,
+    "from": "2026-10-01T00:00:00Z",
     "id": "acme-2026-10",
     "link": "https://acme.example/?utm_source=3x-ui",
     "logo": "/sponsors/logo/acme.png",
@@ -1123,6 +1124,7 @@ export const EXAMPLES: Record<string, unknown> = {
     "sponsors": [
       {
         "enable": true,
+        "from": "2026-10-01T00:00:00Z",
         "id": "acme-2026-10",
         "link": "https://acme.example/?utm_source=3x-ui",
         "logo": "/sponsors/logo/acme.png",

frontend/src/generated/schemas.ts

@@ -4476,6 +4476,12 @@ export const SCHEMAS: Record<string, unknown> = {
         "nullable": true,
         "type": "boolean"
       },
+      "from": {
+        "example": "2026-10-01T00:00:00Z",
+        "format": "date-time",
+        "nullable": true,
+        "type": "string"
+      },
       "id": {
         "example": "acme-2026-10",
         "type": "string"

frontend/src/generated/types.ts

@@ -1028,6 +1028,7 @@ export interface Setting {
 
 export interface Sponsor {
   enable?: boolean | null;
+  from?: string | null;
   id: string;
   link: string;
   logo?: string;

frontend/src/generated/zod.ts

@@ -1091,6 +1091,7 @@ export type Setting = z.infer<typeof SettingSchema>;
 
 export const SponsorSchema = z.object({
   enable: z.boolean().nullable().optional(),
+  from: z.string().nullable().optional(),
   id: z.string(),
   link: z.string(),
   logo: z.string().optional(),

frontend/src/pages/api-docs/endpoints.ts

@@ -240,7 +240,7 @@ export const sections: readonly Section[] = [
         method: 'GET',
         path: '/sponsors',
         summary:
-          'Public. Active paid sponsor placements read from the project sponsors.json (cached for 1h); expired entries are dropped. Logos are proxied by the panel at /sponsors/logo/{name}. Used by the login page and panel sponsor slots.',
+          'Public. Active paid sponsor placements read from the project sponsors.json (cached for 1h); entries outside their from/until window are dropped. Logos are proxied by the panel at /sponsors/logo/{name}. Used by the login page and panel sponsor slots.',
         responseSchema: 'SponsorList',
       },
       {