🤖 fix: improve typography defaults (#636)

_Generated with _

## Summary
- enable standards-based font smoothing defaults (kerning, optical
sizing)
- avoid synthetic bold while preserving synthetic italics with
font-synthesis: style
- add heading ligature defaults and gate text-rendering hints behind
supports

## Testing
- make typecheck

Author: kylecarbs

src/browser/styles/globals.css

@@ -30,6 +30,10 @@
 :root {
   color-scheme: dark;
 
+  font-kerning: normal;
+  font-optical-sizing: auto;
+  font-synthesis: style;
+
   @theme {
     /* Mode Colors */
     --color-plan-mode: hsl(210 70% 40%);
@@ -251,6 +255,19 @@
 }
 
 
+h1,
+h2,
+h3 {
+  font-variant-ligatures: common-ligatures contextual;
+}
+
+@supports (text-rendering: optimizeLegibility) {
+  h1,
+  h2 {
+    text-rendering: optimizeLegibility;
+  }
+}
+
 body {
   background-color: var(--color-background);
   color: var(--color-foreground);