Fix blog build + clear 14 dependabot advisories

Build was failing because the new MDX post tried to `import` the
SuchMoonLaunchStoreButtons component — next-mdx-remote/rsc doesn't
support imports inside .mdx; components must be passed via the
`components` prop. Wire the helper into [slug]/page.tsx and drop the
import line from the .mdx.

Dependency bumps to clear the 14 outstanding Dependabot advisories
(9 high, 4 moderate, 1 low):
- apps/web/next: ^15.5.15 → ^15.5.18 (covers 12 next.js advisories)
- pnpm overrides: pin postcss ^8.5.14 (clears 1117015 XSS via </style>)
- pnpm overrides: pin fast-uri ^3.1.2 (clears 1117870 + 1117884 path
  traversal / host confusion)

pnpm audit: 14 vulnerabilities → 0.

package.json

@@ -29,7 +29,9 @@
       "minimatch": "^9.0.7",
       "picomatch": "^4.0.4",
       "ajv": "^8.17.1",
-      "brace-expansion": "^2.0.3"
+      "brace-expansion": "^2.0.3",
+      "postcss": "^8.5.14",
+      "fast-uri": "^3.1.2"
     }
   }
 }