feat(render+identity): daily render-limit — consume on submit, refund on admin-stop

Business rule: each user has a daily render limit. Admin-stop refunds the used
charge (not the user's fault); a user's own cancel does not.

- identity: ConsumeRenderChargeAsync / RefundRenderChargeAsync on DailyRemainRenderCount
  with lazy daily reset (mig 24: daily_renders_reset_at). Convention: max=0 ⇒ UNLIMITED,
  so existing 0/0 users keep rendering until an admin sets a real limit.
- identity InternalController (service-token): POST /v1/internal/render-charge/{consume,refund}
- render-svc: identityclient + on Create consume (block 429 when limit reached, fail-open
  on identity outage); on admin Stop refund the job owner; user /cancel unchanged
- compose: IDENTITY_URL for render-svc, ServiceToken for identity-svc

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/identity/FlatRender.IdentitySvc/Application/Services/AdminService.cs

@@ -102,6 +102,43 @@ public class AdminService(IdentityDbContext db)
         return new UserCrmResponse(c.Tags, c.Note, c.Status);
     }
 
+    // ── Render charge (daily render limit) — consume / refund ─────────────────
+    // Convention: MaxDailyRenderCount == 0 means UNLIMITED (no enforcement).
+
+    public async Task<(bool Allowed, int Remaining)> ConsumeRenderChargeAsync(Guid userId)
+    {
+        var u = await db.Users.FindAsync(userId);
+        if (u == null) return (false, 0);
+        if (u.MaxDailyRenderCount <= 0) return (true, -1); // unlimited
+
+        // Lazy daily reset (UTC day boundary).
+        var today = DateTime.UtcNow.Date;
+        if (u.DailyRendersResetAt == null || u.DailyRendersResetAt.Value.Date < today)
+        {
+            u.DailyRemainRenderCount = u.MaxDailyRenderCount;
+            u.DailyRendersResetAt = DateTime.UtcNow;
+        }
+
+        if (u.DailyRemainRenderCount <= 0)
+        {
+            await db.SaveChangesAsync(); // persist any reset
+            return (false, 0);
+        }
+        u.DailyRemainRenderCount -= 1;
+        u.UpdatedAt = DateTime.UtcNow;
+        await db.SaveChangesAsync();
+        return (true, u.DailyRemainRenderCount);
+    }
+
+    public async Task RefundRenderChargeAsync(Guid userId)
+    {
+        var u = await db.Users.FindAsync(userId);
+        if (u == null || u.MaxDailyRenderCount <= 0) return; // nothing to refund / unlimited
+        u.DailyRemainRenderCount = Math.Min(u.DailyRemainRenderCount + 1, u.MaxDailyRenderCount);
+        u.UpdatedAt = DateTime.UtcNow;
+        await db.SaveChangesAsync();
+    }
+
     // ── Per-user power-actions ──────────────────────────────────────────────
 
     private async Task<User> RequireUser(Guid id) =>