fix: variations/adapt-recipe silent errors and no-op duplicates

AI adapt/variations flows had no catch on their fetch calls, so a
network failure surfaced as nothing happening rather than an error
toast. They also unconditionally persisted the AI's output even when
it was identical to the source recipe, and the adapt route never
recorded a recipeVariations row (only plain forks did) or enforced
the per-tier recipe-count limit other create paths already check.

v0.39.0

apps/web/lib/changelog.ts

@@ -1,5 +1,5 @@
 // Mirrors CHANGELOG.md at the repo root — update both together.
-export const APP_VERSION = "0.38.0";
+export const APP_VERSION = "0.39.0";
 
 export type ChangelogEntry = {
   version: string;
@@ -11,6 +11,13 @@ export type ChangelogEntry = {
 };
 
 export const CHANGELOG: ChangelogEntry[] = [
+  {
+    version: "0.39.0",
+    date: "2026-07-17 13:30",
+    fixed: [
+      "Adapting/varying a recipe with AI could fail silently (no error shown) on a network hiccup, and could save a byte-for-byte duplicate recipe when the AI's output didn't actually differ from the original — both flows now surface real errors and skip saving when nothing changed. AI-adapted recipes also now show up in recipe history (Forked from…) like forks always have.",
+    ],
+  },
   {
     version: "0.38.0",
     date: "2026-07-17 13:00",