feat: add opt-in anonymous telemetry reporting

Add an opt-in telemetry system that sends anonymised instance
statistics to the public API once per day, which proxies them to
PostHog when `POSTHOG_API_KEY` is configured.

- Add `packages/core/src/telemetry.ts` — `performTelemetryReport`
  and `isTelemetryEnabled`; user and title counts are bucketed
  before sending to avoid exposing exact figures
- Add `getInstanceId()` to `settings.ts` — generates and persists a
  stable UUIDv7 for the instance
- Schedule a daily `telemetryReport` cron job (00:30)
- Add `POST /v1/telemetry` to `apps/public-api`; forwards payload
  to PostHog or returns 204 silently if key is absent
- Add `admin.telemetry` and `admin.toggleTelemetry` oRPC procedures
  for inspecting and toggling the setting
- Expose `instanceId` on `system.publicInfo`

apps/public-api/src/app.ts

@@ -26,4 +26,41 @@ app.get("/v1/version", async (c) => {
   }
 });
 
+app.post("/v1/telemetry", async (c) => {
+  const body = await c.req.json();
+
+  if (!body.instanceId || !body.version) {
+    return c.json({ error: "Missing required fields" }, 400);
+  }
+
+  const posthogKey = process.env.POSTHOG_API_KEY;
+  if (!posthogKey) {
+    return c.body(null, 204);
+  }
+
+  try {
+    await fetch("https://us.i.posthog.com/i/v0/e/", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({
+        api_key: posthogKey,
+        event: "instance_report",
+        distinct_id: body.instanceId,
+        properties: {
+          version: body.version,
+          arch: body.arch,
+          users: body.users,
+          titles: body.titles,
+          ...(body.features ?? {}),
+        },
+      }),
+      signal: AbortSignal.timeout(10_000),
+    });
+  } catch {
+    // Fire-and-forget — don't fail the request if PostHog is down
+  }
+
+  return c.body(null, 204);
+});
+
 export default app;

apps/server/src/cron.ts

@@ -14,6 +14,7 @@ import {
   refreshTvChildren,
 } from "@sofa/core/metadata";
 import { getSetting } from "@sofa/core/settings";
+import { performTelemetryReport } from "@sofa/core/telemetry";
 import { performUpdateCheck } from "@sofa/core/update-check";
 import { db } from "@sofa/db/client";
 import { and, eq, inArray, isNotNull, lt, or } from "@sofa/db/helpers";
@@ -366,6 +367,9 @@ export function startJobs() {
   schedule("updateCheck", "0 */6 * * *", async () => {
     await performUpdateCheck();
   });
+  schedule("telemetryReport", "30 0 * * *", async () => {
+    await performTelemetryReport();
+  });
 
   log.info(`Started ${jobs.size} jobs`);
 }

apps/server/src/orpc/procedures/admin.ts

@@ -9,6 +9,7 @@ import {
   restoreFromBackup,
 } from "@sofa/core/backup";
 import { getSetting, setSetting } from "@sofa/core/settings";
+import { isTelemetryEnabled } from "@sofa/core/telemetry";
 import {
   getCachedUpdateCheck,
   isUpdateCheckEnabled,
@@ -132,6 +133,21 @@ export const toggleUpdateCheck = os.admin.toggleUpdateCheck
     setSetting("updateCheckEnabled", String(input.enabled));
   });
 
+// ─── Telemetry ────────────────────────────────────────────────
+
+export const telemetry = os.admin.telemetry.use(admin).handler(() => {
+  return {
+    enabled: isTelemetryEnabled(),
+    lastReportedAt: getSetting("telemetryLastReportedAt"),
+  };
+});
+
+export const toggleTelemetry = os.admin.toggleTelemetry
+  .use(admin)
+  .handler(({ input }) => {
+    setSetting("telemetryEnabled", String(input.enabled));
+  });
+
 // ─── Jobs ──────────────────────────────────────────────────────
 
 export const triggerJob = os.admin.triggerJob

apps/server/src/orpc/procedures/system.ts

@@ -3,7 +3,11 @@ import {
   isOidcConfigured,
   isPasswordLoginDisabled,
 } from "@sofa/auth/config";
-import { getUserCount, isRegistrationOpen } from "@sofa/core/settings";
+import {
+  getInstanceId,
+  getUserCount,
+  isRegistrationOpen,
+} from "@sofa/core/settings";
 import { isTmdbConfigured } from "@sofa/tmdb/config";
 import { tmdbImageUrl } from "@sofa/tmdb/image";
 import { os } from "../context";
@@ -30,6 +34,7 @@ export const publicInfo = os.system.publicInfo.handler(async () => {
     .filter(Boolean) as string[];
 
   return {
+    instanceId: getInstanceId(),
     tmdbConfigured: isTmdbConfigured(),
     userCount: getUserCount(),
     registrationOpen: isRegistrationOpen(),

apps/server/src/orpc/router.ts

@@ -78,6 +78,8 @@ export const router = os.router({
     toggleRegistration: admin.toggleRegistration,
     updateCheck: admin.updateCheck,
     toggleUpdateCheck: admin.toggleUpdateCheck,
+    telemetry: admin.telemetry,
+    toggleTelemetry: admin.toggleTelemetry,
     triggerJob: admin.triggerJob,
   },
   account: {