feat(ui): headings use self-hosted Jyotisha Serif SC, body stays sans (T2-T5)

- --font-display leads with "Jyotisha Serif SC", then exactly the body
  sans stack; no system 宋体 or generic serif (BUG-737 guards kept).
- serif-sc.css imported from site-styles.ts beside globals.css (root
  layout also serves admin); swap, no preload.
- Long-form report title (.personal-report-md-article h1) takes the
  heading face; deliberate sans headings pinned by a new contract test.
- font-stack-loadable-contract: loadable now includes self-hosted
  @font-face with existing files; "no CJK serif" replaced by
  "leads with Jyotisha Serif SC, never a system 宋体" (brief T3).
- DESIGN §3, BUG-737 note, CHANGELOG, device checklist, PROGRESS.

TASK-serif-headings-20260928 T2-T5.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0199rbQDTsUbCVw84wc8BTFe

frontend/src/app/globals.css

@@ -167,14 +167,14 @@
   --color-element-water: #d3e6e8;
   --shadow-soft: 0 1px 2px rgba(29, 29, 31, .06), 0 8px 20px -18px rgba(29, 29, 31, .2);
   --shadow-elevated: 0 1px 2px rgba(29, 29, 31, .07), 0 12px 28px -16px rgba(29, 29, 31, .18);
-  /* Display and body share one sans stack. The old value led with two Anthropic
-     licensed faces (Tiempos Headline, StyreneB) that this app never loads — no
-     @font-face, nothing in public/, and layout.tsx vendors only Inter — so every
-     CJK heading fell through to Songti SC / SimSun. A Latin-serif-first stack was
-     measured and rejected: the Newsreader latin subset costs 132 KB to serif one
-     wordmark, and it splits mixed headings ("D10 事业盘怎么读") into two scripts.
-     Display rank now comes from weight and tracking, not family. See BUG-737. */
-  --font-display: var(--font-inter, Inter), -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
+  /* Headings (display) lead with the self-hosted "Jyotisha Serif SC" — a
+     sliced Noto Serif SC SemiBold, declared in fonts/serif-sc/serif-sc.css with
+     font-weight 500 700 and font-display: swap, no preload. Until a slice
+     arrives, and for any character outside the 6500 it covers, the heading
+     falls through to the same sans stack as body — never to a system 宋体:
+     no Songti / STSong / SimSun / generic serif may appear here (BUG-737,
+     TASK-serif-headings-20260928). Body text stays sans. */
+  --font-display: "Jyotisha Serif SC", var(--font-inter, Inter), -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
   --font-body: var(--font-inter, Inter), -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
   --font-mono: "JetBrains Mono", "SFMono-Regular", Consolas, monospace;
   --type-display-lg: 48px;
@@ -4118,6 +4118,9 @@ input:not([type="radio"]):not([type="checkbox"]):not([class^="ant-"]):not([class
   overflow-wrap: anywhere;
   padding: var(--space-8) var(--space-7) var(--space-10);
 }
+/* The report title (markdown `#`) is the md view's cover line; it takes the
+   heading face like the document view's `.personal-report-cover h1`. */
+.personal-report-md-article h1 { font-family: var(--font-display); }
 .personal-report-md-article h2,
 .personal-report-md-article h3 { scroll-margin-top: 80px; }
 .personal-report-md-article h2 {

frontend/src/app/site-styles.ts

@@ -1,2 +1,5 @@
 import "./globals.css";
+// Heading face @font-face list, kept out of globals.css (≈18 KB gzip of
+// unicode-range data). Loaded wherever globals.css is, never on admin.
+import "./fonts/serif-sc/serif-sc.css";
 import "./birth-time-choice.css";