Aspect-preserved detail image with full-size download

Photo detail page previously showed a square crop of the source image. Now
generate an aspect-preserved medium JPEG (longest side 1600, quality 88)
and display that on the detail page instead. The original file is linked
from a click-through on the image and from a sidebar 'Full size' download
link.

Also skip regeneration of images/thumbs/medium when the destination is
already at least as new as the source, so a rebuild triggered by editing
one sidecar (or restarting the service) no longer redecodes and rescales
every photo.

static/style.css

@@ -183,21 +183,32 @@ body {
 
 .dlayout {
   display: flex;
+  align-items: stretch;
   border: 1px solid var(--line);
 }
 
 .dimg-wrap {
   flex: 1;
-  aspect-ratio: 1;
+  min-width: 0;
   overflow: hidden;
   background: var(--bg1);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.dimg-wrap a {
+  display: block;
+  max-width: 100%;
+  max-height: 85vh;
 }
 
 .dimg-wrap img {
-  width: 100%;
-  height: 100%;
-  object-fit: cover;
   display: block;
+  max-width: 100%;
+  max-height: 85vh;
+  width: auto;
+  height: auto;
 }
 
 .dsidebar {
@@ -257,6 +268,24 @@ body {
   letter-spacing: 0.06em;
 }
 
+.dfull {
+  margin-top: 14px;
+  padding-top: 14px;
+  border-top: 1px solid var(--line);
+}
+
+.dfull a {
+  font-size: 13px;
+  font-family: monospace;
+  color: var(--aqua);
+  text-decoration: none;
+  letter-spacing: 0.04em;
+}
+
+.dfull a:hover {
+  color: var(--fg2);
+}
+
 /* ── Responsive ────────────────────────────────────────────── */
 
 @media (max-width: 600px) {