fix(blog): hide drafts at the access layer, and back the --drop claim

Review findings on #140.

Drafts were reachable. Posts granted unconditional public read and the
_status filter lived only in the pages that query the collection — which
is a convenience, not a control. Payload's documentation is explicit:
"The `draft` argument alone does not restrict documents with _status:
'draft' from being returned by the API." A direct GET /cms-api/posts
would have handed every unpublished draft to any visitor. Read access
now returns a query constraint for anonymous callers, which is the
documented mechanism.

The --drop claim was asserted across four files while the spec still
listed it as an open question. Now verified rather than assumed:
run_full_migration drops exactly ["school_results", "schools"] by name,
there is no drop_all() or DROP SCHEMA anywhere in backend/, the only
other drop is schema-qualified to marts, and nothing sets search_path.
The guarantee is stronger than schema isolation alone — those two table
names do not exist in Payload — so the claim stands, but it now rests on
cited code. The spec records the evidence and closes the open item.

findPost is wrapped in React's cache(): Next calls generateMetadata and
the page separately for one request, so every post view ran the same
query against Postgres twice.

The bare .lede rule was dead — .prose p scores (0,1,1) and outranks it —
so only .prose .lede ever applied. Removed, with the specificity noted
so the surviving selector is not "simplified" back into a silent
regression.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017YmbBhr8s7GusjDE12hrZM

nextjs-app/__tests__/payload/collections.test.ts

@@ -29,8 +29,14 @@ describe('posts collection', () => {
     expect(slugField).toMatch(/index:\s*true/);
   });
 
-  it('is publicly readable', () => {
-    expect(POSTS).toMatch(/access:\s*\{\s*read:\s*\(\)\s*=>\s*true/);
+  it('hides drafts from anonymous readers at the access layer', () => {
+    // Payload's docs are explicit: "The `draft` argument alone does not
+    // restrict documents with _status: 'draft' from being returned by the
+    // API." The blog pages' where-clause is not enforcement — a direct GET
+    // /cms-api/posts would return unpublished drafts to anyone. Access
+    // control returning a query constraint is the only thing that stops it.
+    expect(POSTS).toMatch(/_status:\s*\{\s*equals:\s*'published'\s*\}/);
+    expect(POSTS).toMatch(/if\s*\(req\.user\)\s*return true/);
   });
 
   it('revalidates the post page when a post changes or is deleted', () => {