chore: enable TypeScript strict mode and drop dead Payload scripts

The shared base tsconfig had strict off, so null-safety and union narrowing
were not checked. Strict is now on for apps/web with 5 small typing fixes.
check-db.ts and migrate-drafts.js depended on Payload, which is no longer a
dependency, and are removed. CLAUDE.md no longer claims Payload.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

apps/web/app/(site)/blog/[slug]/page.tsx

@@ -93,7 +93,7 @@ export default async function BlogPostPage({
             <Reveal delay={0.4} width="100%">
               {post.tags && post.tags.length > 0 && (
                 <div className="flex flex-wrap gap-2 mb-10 md:mb-12">
-                  {post.tags?.map((tag) => (
+                  {post.tags?.map((tag: string) => (
                     <span
                       key={tag}
                       className="px-2.5 py-1 bg-slate-50 border border-slate-100 rounded text-[9px] md:text-[10px] font-mono text-slate-500 uppercase tracking-widest"
@@ -106,7 +106,7 @@ export default async function BlogPostPage({
 
               <div className="article-content max-w-none">
                 <TableOfContents />
-                  <MDXContent code={post.mdxContent || ""} />
+                <MDXContent code={post.mdxContent || ""} />
               </div>
             </Reveal>
           </div>