feat(shots): previous/next shot navigation on the shot page

Prev/next buttons beside the breadcrumb walk the project's shot list in
the same order as the Shots tab. The ordering now lives in
lib/shot-order.ts, shared by the project page and the shot API.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/shot-order.ts

@@ -0,0 +1,36 @@
+// The order shots appear in on the project page's Shots tab. Shared with the
+// shot detail page so its previous/next navigation walks the same list.
+
+type OrderableShot = {
+  episode?: string | null;
+  scene: string;
+  shotNumber: number;
+  shotGroup?: { name: string } | null;
+};
+
+export function sortShotsForList<T extends OrderableShot>(shots: T[], projectType: string): T[] {
+  // Episodic: episode → scene → shotNumber
+  if (projectType === "EPISODIC") {
+    return [...shots].sort((a, b) => {
+      const ea = a.episode ?? "";
+      const eb = b.episode ?? "";
+      if (ea !== eb) return ea.localeCompare(eb, undefined, { numeric: true });
+      if (a.scene !== b.scene) return a.scene.localeCompare(b.scene, undefined, { numeric: true });
+      return a.shotNumber - b.shotNumber;
+    });
+  }
+
+  // Standard with custom groups: group → scene → shotNumber, ungrouped last
+  if (projectType === "STANDARD" && shots.some((s) => s.shotGroup)) {
+    return [...shots].sort((a, b) => {
+      const ga = a.shotGroup?.name ?? "￿";
+      const gb = b.shotGroup?.name ?? "￿";
+      if (ga !== gb) return ga.localeCompare(gb, undefined, { numeric: true });
+      if (a.scene !== b.scene) return a.scene.localeCompare(b.scene, undefined, { numeric: true });
+      return a.shotNumber - b.shotNumber;
+    });
+  }
+
+  // Otherwise the list keeps the query's createdAt order
+  return shots;
+}