contact messages: trigger button uses the navbar font and weight

Nav family/weight become --font-nav/--nav-weight (base defaults body/400; nitro heading/700, corporate 600), referenced by both #nav and .contact-trigger. The button keeps the article's size and line-height.

frontend/src/assets/pagerite.css

@@ -72,6 +72,10 @@
   --font-heading: var(--font-source-serif);
   /* The brand follows the heading font unless overridden separately. */
   --font-brand: var(--font-heading);
+  /* Navbar typography (family and weight only — size/letter-case stay
+     per-theme #nav rules); the {contact:} trigger button matches it. */
+  --font-nav: var(--font-body);
+  --nav-weight: 400;
   --font-code: var(--font-fira-code);
   /* Target x-height ratio for code text: set to the body font's ratio
      (here Source Sans 3's 0.478) so font-size-adjust can scale the code
@@ -258,6 +262,8 @@ body {
 
 /* Nav overlaid at the bottom of the banner */
 #nav {
+  font-family: var(--font-nav);
+  font-weight: var(--nav-weight);
   font-size: 1.3em;
   padding: 0.35rem 1.25rem;
 }
@@ -905,7 +911,11 @@ article {
   position: relative;
   margin: 0.3em 0.1em;
   padding: 0.35em 1.1em;
-  font: inherit;
+  /* Same font and weight as the navbar, size/leading as the article text. */
+  font-size: inherit;
+  line-height: inherit;
+  font-family: var(--font-nav);
+  font-weight: var(--nav-weight);
   color: var(--ink, var(--bg));
   background: var(--accent);
   border: 1px solid var(--accent);

pagerite/themes/corporate/theme.css

@@ -16,6 +16,7 @@
   --line: #12203f14;
   --font-body: var(--font-inter);
   --font-heading: var(--font-montserrat);
+  --nav-weight: 600;
   --code-x-height: 0.546; /* Inter's x-height ratio */
 }
 
@@ -54,7 +55,6 @@
 
 #nav {
   font-size: 1.05em;
-  font-weight: 600;
   letter-spacing: 0.04em;
   text-transform: uppercase;
   text-shadow: none;

pagerite/themes/nitro/theme.css

@@ -41,6 +41,8 @@
 
   --font-body: var(--font-montserrat);
   --font-heading: var(--font-literata);
+  --font-nav: var(--font-heading);
+  --nav-weight: 700;
   --code-x-height: 0.517; /* Montserrat's x-height ratio */
   /* Neutral grey selection instead of the accent tint: accent-colored
      text (h2, links, markers) stays readable on it in both schemes. */
@@ -86,9 +88,7 @@
 }
 
 #nav {
-  font-family: var(--font-heading);
   font-size: 0.95em;
-  font-weight: 700;
   letter-spacing: 0.08em;
   text-transform: uppercase;
   /* Racing tab: sitting at the bottom of the banner, with a bezier clip —