Arrow icons, cascading own CSS, a preload for the hero image, and EB Solar

Built while setting up the redesign of ebsolar.de as the sixth local
installation (scripts/seed-ebsolar.php, reset-ebsolar.sh, ports 8096/8097).
The rebuild surfaced four things in the core:

- The icon set knows three arrows now: arrow-right, arrow-left,
  arrow-up-right. The button block and the post navigation render them as
  inline SVG inside the same aria-hidden span as before, so a template that
  hides the arrow with "& span{display:none}" keeps working. Until now the
  arrow was a text glyph that looked different in every font. Umut: "bei
  alle Projekte bzw bei allen möchte ich dieses emoji icon weg haben".

- Own CSS with the same nested selector twice kept only the last rule.
  "& .post-card{border:0}" followed by "& .post-card{transform:none}" lost
  the border - silently, which brought the core's card frame back on the
  project grid. The parser now joins the declarations in source order, as
  CSS does; the same for "&{…}" next to the element's own properties.

- The eager image over the fold was not preloaded. The background image of
  the first section has had a preload link for a while; a plain <img> was
  found only after the stylesheet was parsed, and that round trip went
  straight into LCP. PageController::heroImage() now writes the same src,
  srcset and sizes the block template writes, and page.html.twig emits the
  link - unless a background image is already preloaded.

- Measured on the way: an entrance effect on the LCP element costs about
  900 ms of render delay. The EB Solar hero image therefore has none.

Tests: 581 green, the icon test accepts quoted keys, two cases for the CSS
cascade, the preload asserted in the big-picture test.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.claude/launch.json

@@ -79,6 +79,26 @@
       ],
       "port": 8094
     },
+    {
+      "name": "ebsolar",
+      "runtimeExecutable": "powershell",
+      "runtimeArgs": [
+        "-NoProfile",
+        "-Command",
+        "$env:APP_ENV='dev'; $env:DATABASE_URL='sqlite:///C:/Django Project/KantSites/var/ebsolar.db'; $env:MEDIA_DIRECTORY='C:/Django Project/KantSites/var/ebsolar-media'; $env:SITE_ORIGIN='http://127.0.0.1:8096'; & C:/php84/php.exe -d upload_max_filesize=8M -d post_max_size=10M -d memory_limit=256M -S 127.0.0.1:8096 -t public bin/dev-router.php"
+      ],
+      "port": 8096
+    },
+    {
+      "name": "ebsolar-prod",
+      "runtimeExecutable": "powershell",
+      "runtimeArgs": [
+        "-NoProfile",
+        "-Command",
+        "$env:APP_ENV='prod'; $env:APP_DEBUG='0'; $env:DATABASE_URL='sqlite:///C:/Django Project/KantSites/var/ebsolar.db'; $env:MEDIA_DIRECTORY='C:/Django Project/KantSites/var/ebsolar-media'; $env:SITE_ORIGIN='http://127.0.0.1:8097'; & C:/php84/php.exe -d upload_max_filesize=8M -d post_max_size=10M -d memory_limit=256M -S 127.0.0.1:8097 -t public bin/dev-router.php"
+      ],
+      "port": 8097
+    },
     {
       "name": "immobilien-deeg-prod",
       "runtimeExecutable": "powershell",