site: upgrade Astro 5 → 7

- astro 7.0.7, @astrojs/mdx 7, sitemap 3.7, rss 4.0.19, check 0.9.9
- trailingSlash 'always' → 'ignore': Astro 7 generates prerender paths for
  dynamic extension endpoints (/categories/<c>/rss.xml) with a trailing
  slash under 'always' but builds their route patterns without one, so the
  build fails with "Missing parameter"; directory-format output is
  identical either way. Also removes the now-unneeded dev feed-slash shim.
- compressHTML: true pinned to keep pre-v7 whitespace behavior
- zod 4: import z from 'astro/zod' (astro:content re-export deprecated),
  z.string().url() → z.url()
- npm audit fix (fast-uri, fast-xml-builder, yaml)

Claude-Session: https://claude.ai/code/session_01WZaczDJjL3xZ3u5spsN5AL

package.json

@@ -15,11 +15,11 @@
     "astro": "astro"
   },
   "dependencies": {
-    "@astrojs/check": "^0.9.4",
-    "@astrojs/mdx": "^4.3.14",
-    "@astrojs/rss": "^4.0.12",
-    "@astrojs/sitemap": "^3.6.0",
-    "astro": "^5.1.1",
+    "@astrojs/check": "^0.9.9",
+    "@astrojs/mdx": "^7.0.2",
+    "@astrojs/rss": "^4.0.19",
+    "@astrojs/sitemap": "^3.7.3",
+    "astro": "^7.0.7",
     "sharp": "^0.34.0",
     "typescript": "^5.7.2"
   }