fix(og): unify context-saving wordmark with Master + Insight

Same typography pass on the dark surface banner:
- font-weight 600 → 700
- font-size 120px → 104px
- letter-spacing -.04em → -.045em
- cursor 34×100 → 31×96 (.30em × .92em proportional)

All three OG banners now share one wordmark system.

web/og/context-saving-og.html

@@ -32,10 +32,10 @@
   .dot{display:inline-block;width:6px;height:6px;border-radius:50%;background:#10b981;margin-right:6px;vertical-align:middle;box-shadow:0 0 10px rgba(16,185,129,.7)}
   .meta{font-size:12px;color:#6b7a8d;letter-spacing:.08em}
   .stack{position:relative;z-index:2}
-  .wordmark{display:inline-flex;align-items:baseline;font-weight:600;font-size:120px;line-height:.95;letter-spacing:-.04em;color:#fafafa}
+  .wordmark{display:inline-flex;align-items:baseline;font-weight:700;font-size:104px;line-height:.95;letter-spacing:-.045em;color:#fafafa}
   .wordmark .prompt{color:#6b7a8d;margin-right:.3em;font-weight:400}
   .wordmark .dash{color:#475569}
-  .cursor{display:inline-block;width:34px;height:100px;background:#10b981;margin-left:12px;transform:translateY(8px);box-shadow:0 0 24px rgba(16,185,129,.4)}
+  .cursor{display:inline-block;width:31px;height:96px;background:#10b981;margin-left:14px;transform:translateY(6px);box-shadow:0 0 24px rgba(16,185,129,.4)}
   .tagline{margin-top:30px;font-family:'IBM Plex Sans',sans-serif;font-style:normal;font-weight:600;font-size:42px;line-height:1.15;color:#fafafa;letter-spacing:-.025em;max-width:980px}
   .tagline em{font-style:normal;color:#10b981;font-weight:600}
   .sub{margin-top:18px;font-family:'IBM Plex Sans',sans-serif;font-size:18px;line-height:1.5;color:#94a3b8;max-width:900px;font-weight:400}