experimental: portfolio features (justified layout, unlisted pages, captions, per-album grid, focal point, nav links, cover hero) (#431)

## Was ist das?

Sieben neue Portfolio-Features, alle als **experimental** gekennzeichnet
— in YAML-Kommentaren, Admin-Panel-Labels und Commit-Scopes, damit sie
einzeln nachvollziehbar und revertierbar bleiben.

## Features (je ein Commit)

| Commit | Feature |
| --- | --- |
| `justified rows gallery layout` | Neues Grid-Layout `justified`:
zeilenbasiert, gleiche Höhen, volle Breite — Flexbox ohne JS-Messung,
letzte Zeile bleibt natürlich klein |
| `hide subpages from navigation` | `hidden: true`: Seite aus
Nav/Homepage raus, per Direktlink erreichbar — im Gegensatz zu `enabled:
false` (404) |
| `lightbox captions` | Immich-Asset-Description als Bildunterschrift im
Info-Panel; EXIF-Route liefert bei `exifOnHover: false` jetzt nur noch
die Caption statt 403 |
| `per-album grid overrides` | `grid:` pro Album-Eintrag, Präzedenz
global < Subpage < Album |
| `per-album cover focal point` | `coverPosition:` → `object-position`
auf Cover-Karten, strikt validiert |
| `external links in header navigation` | `navLinks:` in settings.yaml,
nur http(s), sanitisiert |
| `cover splash hero style` | `heroStyle: cover`: Fullscreen-Splash mit
Enter-Link ins Portfolio |

Alle Optionen sind im Admin-Panel editierbar (PageBuilder /
SettingsEditor).

## Tests

- 356 Unit-Tests grün (13 neue: deriveGallery hidden/grid/coverPosition,
sanitizeNavLinks, EXIF-Route-Captions, justified-Layout-Validierung)
- `npx tsc --noEmit`: 0 Fehler
- `npm run build`: sauber
- Justified-Zeilenmathematik und Cover-Splash per Browser-Harness
visuell/numerisch verifiziert (volle Zeilen enden exakt an der
Containerkante, letzte Zeile bleibt natürlich)

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: ralksta <ralksta@users.noreply.github.com>
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: lancetm714 <108419425+lancetm714@users.noreply.github.com>

app/globals.css

@@ -244,6 +244,76 @@
   overflow: hidden;
 }
 
+/* ── Cover / Splash hero (EXPERIMENTAL) ───────────── */
+/* Fullscreen welcome page: one image, the title, a single Enter link. */
+.hero--cover {
+  position: relative;
+  min-height: calc(100vh - 56px);
+  min-height: calc(100dvh - 56px);
+  overflow: hidden;
+}
+
+.hero--cover > span,
+.hero--cover > img {
+  position: absolute !important;
+  inset: 0;
+  width: 100% !important;
+  height: 100% !important;
+  object-fit: cover;
+}
+
+.hero__cover-overlay {
+  position: absolute;
+  inset: 0;
+  z-index: 2;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  text-align: center;
+  padding: 64px 40px;
+  background: radial-gradient(ellipse at center, rgba(0, 0, 0, 0.5) 0%, rgba(0, 0, 0, 0.1) 75%);
+  color: #fff;
+}
+
+.hero--cover .hero__title,
+.hero--cover .hero__subtitle {
+  color: #fff;
+}
+
+.hero__cover-enter {
+  display: inline-flex;
+  align-items: center;
+  gap: 10px;
+  margin-top: 36px;
+  padding: 12px 32px;
+  border: 1px solid rgba(255, 255, 255, 0.7);
+  border-radius: var(--radius-lg, 4px);
+  color: #fff;
+  font-family: var(--font-caption);
+  font-size: 0.85rem;
+  letter-spacing: 0.18em;
+  text-transform: uppercase;
+  text-decoration: none;
+  transition:
+    background var(--transition-normal),
+    color var(--transition-normal);
+}
+
+.hero__cover-enter:hover,
+.hero__cover-enter:focus-visible {
+  background: #fff;
+  color: #000;
+}
+
+.hero__cover-enter-arrow {
+  transition: transform var(--transition-normal);
+}
+
+.hero__cover-enter:hover .hero__cover-enter-arrow {
+  transform: translateX(4px);
+}
+
 /* HeroCarousel images fill the entire container */
 .hero--fullbleed > span,
 .hero--fullbleed > img {
@@ -1084,6 +1154,55 @@
   }
 }
 
+/* ── Justified Rows Layout (EXPERIMENTAL) ───────── */
+/* Row-based justified layout: every row fills the container width, all
+   images in a row share the same height, aspect ratios stay intact.
+   Flex sizing (grow = aspect ratio) lives inline on the .fade-in wrapper. */
+.photo-grid--justified {
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--grid-gap, 12px);
+  column-count: unset;
+  /* More columns → shorter rows, mirroring the density of the other layouts */
+  --grid-row-height: calc(900px / var(--grid-columns, 3));
+}
+
+/* Filler that soaks up leftover space so the last row keeps natural sizes
+   instead of stretching a lone image to full width */
+.photo-grid--justified::after {
+  content: '';
+  flex-grow: 999999;
+  min-width: 0;
+}
+
+.photo-grid--justified > .fade-in {
+  height: var(--grid-row-height);
+  min-width: 0;
+}
+
+.photo-grid--justified .photo-grid__item {
+  height: 100%;
+  width: 100%;
+  margin-bottom: 0;
+  /* The base .photo-grid__item rule forces aspect-ratio from the grid
+     setting. Combined with height: 100% that pins the item width to
+     height × ratio, so it never fills the flex-grown wrapper and rows end
+     ragged. The wrapper's flex sizing is the only geometry source here. */
+  aspect-ratio: unset;
+}
+
+@media (max-width: 1024px) {
+  .photo-grid--justified {
+    --grid-row-height: 240px;
+  }
+}
+
+@media (max-width: 640px) {
+  .photo-grid--justified {
+    --grid-row-height: 160px;
+  }
+}
+
 .photo-grid__item img {
   width: 100%;
   height: 100%;