fix: add Content-Type: application/json to store-github requests

GitHub API infers JSON without Content-Type; Gitea requires it explicitly.
Without the header, Gitea cannot parse the POST/PUT body and returns 422
Unprocessable Entity on all content write operations.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/patch-store-github-content-type.mjs

@@ -0,0 +1,45 @@
+/**
+ * Patch: add Content-Type: application/json to store-github #client requests.
+ *
+ * The #client method only sets `accept` and `authorization` headers.
+ * GitHub's API infers JSON from the body without Content-Type; Gitea's API
+ * requires an explicit Content-Type: application/json header on POST/PUT
+ * requests — without it the body is not parsed and Gitea returns 422
+ * Unprocessable Entity.
+ */
+
+import { readFile, writeFile, access } from "node:fs/promises";
+
+const TARGET = "node_modules/@indiekit/store-github/index.js";
+const MARKER = "// [patch] store-github-content-type";
+
+const OLD = `          accept: "application/vnd.github+json",
+          authorization: \`token \${token}\`,`;
+
+const NEW = `          accept: "application/vnd.github+json",
+          authorization: \`token \${token}\`,
+          "content-type": "application/json", ${MARKER}`;
+
+async function exists(p) {
+  try { await access(p); return true; } catch { return false; }
+}
+
+if (!(await exists(TARGET))) {
+  console.log(`[postinstall] store-github-content-type: target not found, skipping`);
+  process.exit(0);
+}
+
+const source = await readFile(TARGET, "utf8");
+
+if (source.includes(MARKER)) {
+  console.log("[postinstall] store-github-content-type: already patched");
+  process.exit(0);
+}
+
+if (!source.includes(OLD)) {
+  console.warn("[postinstall] store-github-content-type: snippet not found — skipping");
+  process.exit(0);
+}
+
+await writeFile(TARGET, source.replace(OLD, NEW), "utf8");
+console.log(`[postinstall] store-github-content-type: patched ${TARGET}`);