feat(render): plan-gate quality tiers — free=360p watermarked, paid=all

Monetization gate for the template render flow:
- render-quality.ts: single source of truth (free -> 360p only +
  watermark; pro/business -> 540p..4K, no watermark).
- /api/render: server-authoritative gate — rejects >360p for free
  users with 403 quality_locked; passes a watermark flag through
  createRenderJob -> /v1/renders (render-svc passthrough, wired later).
- /api/render/limits: GET endpoint exposing the user's allowed tiers
  and watermark state to the studio.
- render page: locks higher tiers for free users (dashed + lock badge,
  click routes to /pricing), clamps the selected resolution down,
  shows the "free = 360p + watermark, upgrade" notice, and handles the
  403 quality_locked response.

AI-video "no free preview" rule is a future hook (no AI gen yet).
Watermark rendering (ffmpeg drawtext on the node) is a follow-up.

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

src/lib/render-quality.ts

@@ -0,0 +1,31 @@
+/**
+ * Render quality policy (monetization gate).
+ *
+ *   Free plan   → 360p only, watermarked preview.
+ *   Pro/Business → every resolution (540p–4K), no watermark.
+ *
+ * (AI-generated videos will have NO free preview at all — pay/credits before the
+ * result is shown. That rule belongs in the AI-video feature when it's built;
+ * this module covers the normal template render flow.)
+ */
+import type { PlanId } from "@/lib/plans";
+import type { RenderSettings } from "@/lib/render-schemas";
+
+export type Resolution = RenderSettings["resolution"]; // "360p" | "540p" | "720p" | "1080p" | "4K"
+
+export const FREE_RESOLUTION: Resolution = "360p";
+export const ALL_RESOLUTIONS: Resolution[] = ["360p", "540p", "720p", "1080p", "4K"];
+
+/** Resolutions a plan may render at. Free = 360p only; any paid plan = all. */
+export function allowedResolutions(plan: PlanId): Resolution[] {
+  return plan === "free" ? [FREE_RESOLUTION] : ALL_RESOLUTIONS;
+}
+
+export function isResolutionAllowed(plan: PlanId, res: Resolution): boolean {
+  return allowedResolutions(plan).includes(res);
+}
+
+/** Free renders get a watermarked preview; paid plans get clean output. */
+export function isWatermarked(plan: PlanId): boolean {
+  return plan === "free";
+}