style(site): annotation headings in part-page file-blocks match TOC title scale

The h2/h3 inside .annotation-card / .annotation-md (the prose
column alongside each code chunk on part pages) was falling
through to the global h1/h2 rules (22px bold / 26px bold). A
meander annotation that happens to include an h2 like "Known
Limitation: instanceof checks…" rendered as a hero headline
inside what's supposed to be quiet margin prose.

Normalize h1-h4 inside both .annotation-card and .annotation-md
to 18px / 600 — same scale as .doc-body headings and
.wt-contents-title. Hierarchy comes from margin (16 / 24 / 20 /
16) alone; size stays flat so the rhythm matches the rest of
the site.

Author: jdalton

overrides.css

@@ -1623,14 +1623,45 @@ body.col-resizing * {
   padding: 0;
 }
 
-.annotation-card h3 {
-  margin: 0 0 10px;
+/* Every annotation heading (h1-h4) sits at the same 18px / 600
+ * scale as doc-page titles + the home TOC. Hierarchy comes from
+ * margin alone; size + weight stay flat so the prose rhythm
+ * matches what readers see everywhere else on the site. */
+.annotation-card h1,
+.annotation-card h2,
+.annotation-card h3,
+.annotation-card h4,
+.annotation-md h1,
+.annotation-md h2,
+.annotation-md h3,
+.annotation-md h4 {
   font-size: 18px;
-  font-weight: 700;
+  font-weight: 600;
   letter-spacing: -0.01em;
+  line-height: 1.3;
   color: var(--ink);
 }
 
+.annotation-card h1,
+.annotation-md h1 {
+  margin: 0 0 16px;
+}
+
+.annotation-card h2,
+.annotation-md h2 {
+  margin: 24px 0 12px;
+}
+
+.annotation-card h3,
+.annotation-md h3 {
+  margin: 20px 0 10px;
+}
+
+.annotation-card h4,
+.annotation-md h4 {
+  margin: 16px 0 8px;
+}
+
 .annotation-md {
   color: var(--body);
   font-size: 15px;