feat(render): full-screen render page, one-active-render limit, app-wide progress

Concurrent-render ceiling (a user runs 1 render at a time unless granted more):
- Identity: TokenService emits max_renders claim from User.ParallelRenderingCeiling
- Identity: admin POST /v1/users/{id}/render-slots (AdminService.SetRenderSlotsAsync,
  clamped 1..50) — gamification or admin raises a user's ceiling
- render-svc: middleware reads max_renders (default 1); CreateJob rejects with 409
  active_render_limit when active jobs >= ceiling
- render-svc: db.CountActiveJobs + ListActiveJobs; GET /v1/renders/active returns
  in-flight renders + can_start_new

Full-screen render page (replaces the modal):
- /studio/render/[projectId]: config (resolution/fps) → live preview + progress →
  download; resumes this project's in-flight render on mount; blocks when another
  render is active; reads ?preset=
- StudioTopBar export menu now navigates to the page; RenderModal deleted (dead)

App-wide minimal progress:
- GlobalRenderProgress pill mounted in the locale layout for authed users; polls
  /api/render/active every 4s, shows thumbnail + step + % on every page, click →
  the render page; hidden on the render page and when idle

Admin: UserActions gains a "concurrent render slots" control.

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

services/render/internal/middleware/auth.go

@@ -3,6 +3,7 @@ package middleware
 import (
 	"fmt"
 	"net/http"
+	"strconv"
 	"strings"
 
 	"github.com/flatrender/render-svc/internal/models"
@@ -12,10 +13,11 @@ import (
 )
 
 const (
-	CtxUserID   = "user_id"
-	CtxTenantID = "tenant_id"
-	CtxIsAdmin  = "is_admin"
-	CtxRole     = "role"
+	CtxUserID     = "user_id"
+	CtxTenantID   = "tenant_id"
+	CtxIsAdmin    = "is_admin"
+	CtxRole       = "role"
+	CtxMaxRenders = "max_renders"
 )
 
 func JWTAuth(secret string) gin.HandlerFunc {
@@ -54,10 +56,25 @@ func JWTAuth(secret string) gin.HandlerFunc {
 		}
 		role, _ := claims["role"].(string)
 
+		// max_renders: concurrent-render ceiling. Identity emits it as a string;
+		// also accept a JSON number. Default 1 when absent/unparseable.
+		maxRenders := 1
+		switch v := claims["max_renders"].(type) {
+		case string:
+			if n, err := strconv.Atoi(v); err == nil && n > 0 {
+				maxRenders = n
+			}
+		case float64:
+			if v >= 1 {
+				maxRenders = int(v)
+			}
+		}
+
 		c.Set(CtxUserID, userID)
 		c.Set(CtxTenantID, tenantID)
 		c.Set(CtxIsAdmin, isAdmin)
 		c.Set(CtxRole, role)
+		c.Set(CtxMaxRenders, maxRenders)
 		c.Next()
 	}
 }
@@ -111,3 +128,16 @@ func GetTenantID(c *gin.Context) uuid.UUID {
 	id, _ := v.(uuid.UUID)
 	return id
 }
+
+// GetMaxRenders returns the user's concurrent-render ceiling (default 1).
+func GetMaxRenders(c *gin.Context) int {
+	v, ok := c.Get(CtxMaxRenders)
+	if !ok {
+		return 1
+	}
+	n, _ := v.(int)
+	if n < 1 {
+		return 1
+	}
+	return n
+}