fix redirect targets missing base path on GitHub Pages

Astro prepends base to redirect sources but not targets, so the
meta-refresh URL was /<year>/<slug> instead of /python-insider-blog/...

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

Author: JacobCoffee

astro.config.ts

@@ -9,10 +9,16 @@ import remarkPythonRefs from "./src/plugins/remark-python-refs";
 const isDev = process.env.NODE_ENV === "development" || process.argv.includes("dev");
 
 // Load redirects generated by the migration script
+// Astro prepends `base` to the redirect source but not the target,
+// so we prepend it ourselves for non-root deployments.
+const base = isDev ? "" : "/python-insider-blog";
 let redirects: Record<string, string> = {};
 try {
   const redirectsPath = new URL("./src/data/redirects.json", import.meta.url);
-  redirects = JSON.parse(fs.readFileSync(redirectsPath, "utf-8"));
+  const raw: Record<string, string> = JSON.parse(fs.readFileSync(redirectsPath, "utf-8"));
+  for (const [from, to] of Object.entries(raw)) {
+    redirects[from] = `${base}${to}`;
+  }
 } catch {
   // No redirects file yet (run migration first)
 }