show author on articles (single page byline + journal listing)

- Single page: 'von {Author} · {Date}' byline directly under H1 in
  mono, editorial-style. Falls back to site.Params.author.name.
- Journal listing: author appended to existing meta row.
- Bottom .time line cleaned: only renders if there's reading time
  or a meaningful lastmod, to avoid an empty meta strip.

Per-page override via 'author' frontmatter field; until set,
everything is credited to the site default author.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

assets/css/custom.css

@@ -253,6 +253,8 @@ a:hover {
 }
 .journal-section { color: var(--accent); font-weight: 500; }
 .journal-date { font-variant-numeric: tabular-nums; }
+.journal-author { color: var(--color-text-primary); font-weight: 500; }
+.journal-author::before { content: "von "; color: var(--color-text-muted); font-weight: 400; }
 
 .journal-title {
   font-family: var(--font-family-display);
@@ -434,12 +436,25 @@ a:hover {
   line-height: 1.15;
   margin: 0 0 var(--spacing-xs);
 }
+.single-byline {
+  font-family: var(--font-family-mono);
+  font-size: 0.85rem;
+  color: var(--color-text-muted);
+  margin: 0 0 var(--spacing-xs);
+  display: flex;
+  flex-wrap: wrap;
+  gap: 0.6rem;
+  align-items: baseline;
+}
+.byline-author { color: var(--color-text-primary); font-weight: 500; }
+.byline-date { font-variant-numeric: tabular-nums; }
+
 .single-summary {
   font-family: var(--font-family-serif);
   font-style: italic;
   font-size: 1.02rem;
   line-height: 1.45;
-  margin: 0;
+  margin: var(--spacing-xs) 0 0;
   max-width: 55ch;
 }
 .single-content h2 {