republik-style redesign: dark masthead, hero block, palette, pills

- Dark full-bleed masthead with serif wordmark and stacked nav
- Hero entry treatment: full-bleed image bg with gradient overlay
- Per-section color system (data-section) + per-post override (data-color)
- Japanese accent palette (ajisai, sakura, suna, ichigo, yuyake, sora,
  kusa, kori, amagumo, yuki) — set via `color:` in front matter
- Tag pills replace hashtag-style tags; rendered as sibling of card link
  to avoid invalid nested <a> elements
- Single article: clean Republik-style header, no section rubric,
  tags as pills at bottom
- Cover image support (`cover_image:` in front matter):
    - wide mode: full-card banner above text
    - icon mode: small thumbnail right of text with colored card bg
- Library subsection header redesigned with section-colored stripe
- Dates use Swiss DD.MM.YYYY display (ISO retained in datetime attr)
- Custom Tokyo metro photo as demo cover image

layouts/library/list.html

@@ -6,7 +6,8 @@
       {{/* Library root: Atlas — gruppiert nach Untersection */}}
       <section class="atlas">
         {{ range .Sections.ByWeight }}
-          <article class="atlas-section">
+          {{ $section := path.Base .RelPermalink }}
+          <article class="atlas-section" data-section="{{ $section }}">
             <h2><a href="{{ .RelPermalink }}">{{ .Title }}</a></h2>
             {{ with .Params.description }}<p class="text-muted">{{ . }}</p>{{ end }}
             <ul class="atlas-list">
@@ -37,7 +38,13 @@
       </section>
     {{ else }}
       {{/* Library subsection: chronologisch */}}
-      <div class="time-list">
+      {{ $section := path.Base .RelPermalink }}
+      <header class="section-header" data-section="{{ $section }}">
+        <p class="section-rubric">Library</p>
+        <h1 class="section-title">{{ .Title }}</h1>
+        {{ with .Params.description }}<p class="section-description">{{ . }}</p>{{ end }}
+      </header>
+      <div class="time-list" data-section="{{ $section }}">
         <ul>
           {{ range .RegularPages.ByDate.Reverse }}
             <li class="list-item">