fix(design): stop synthesizing bold on Hedvig display headings (#1555)

* fix(design): stop synthesizing bold on Hedvig display headings

Hedvig Letters Serif ships weight 400 only, but the h1-h3 base rule
forced font-weight 500 and DialogTitle/SheetTitle stacked font-semibold
on top, so every display heading rendered browser-synthesized bold: the
smudged heavy look on dialog titles and page headings. Drop the base
rule to 400, remove the weight utilities from the title primitives, and
sweep the 41 files that hand-set font-medium/semibold/bold on serif
headings (a pattern design.md already forbids). Headings that opt into
font-sans keep their weight.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(design): drop empty className left by the weight sweep

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

components/docs/DocsLayout.tsx

@@ -61,7 +61,7 @@ export function DocsLayout({ currentPath, children }: DocsLayoutProps) {
           <div className="sticky top-24 space-y-8">
             {DOCS_NAV.map((section) => (
               <div key={section.label}>
-                <h3 className="text-[11px] font-medium uppercase tracking-wider text-muted-foreground mb-2 px-3">
+                <h3 className="text-[11px] uppercase tracking-wider text-muted-foreground mb-2 px-3">
                   {section.label}
                 </h3>
                 <ul className="space-y-px">