Solution detail page and a single LinkResolver

Closes two annex items that turned out to be the same defect seen from two
sides: markets could link to a detail page, solutions could not, and the code
that turns a page uid into a URL existed four times over.

detail_page for Solution (B-11)
- ext_tables.sql, TCA (group on pages, maxitems 1, in showitem behind slug)
  and Domain\Model\Solution mirror the Market field exactly
- SolutionShowJsonRenderer emits detailUrl
- ModelcardJsonRenderer serialized no detailUrl at all: its shared
  market|solution branch never carried the field. Market modelcards therefore
  gain a link here too, not just solutions.

Service\LinkResolver (B-12)
- one implementation replaces four private copies (Market list/show, Usecase
  list/show). The copies had drifted: Market returned null on failure, Usecase
  an empty string. The contract is now explicit -- null means "no link".
- Usecase keeps a thin resolvePageUrl() wrapper appending ?? '', because it
  concatenates paths and a null would tear the strings apart.
- LocationsJsonRenderer and NewsJsonRenderer stay out on purpose: they resolve
  a full parameter construct resp. slug paths plus canonical, which is not
  page-uid-to-URL and does not fit the same contract.

Requires on the server, the column exists in code only:
    vendor/bin/typo3 database:updateschema "*.add,*.change"
    vendor/bin/typo3 cache:flush

packages/vitec/Classes/UserFunc/UsecaseShowJsonRenderer.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace Evomedien\Vitec\UserFunc;
 
 use Doctrine\DBAL\ParameterType;
+use Evomedien\Vitec\Service\LinkResolver;
 use Evomedien\Vitec\Service\UsecaseSerializer;
 use TYPO3\CMS\Core\Attribute\AsAllowedCallable;
 use TYPO3\CMS\Core\Database\ConnectionPool;
@@ -153,14 +154,14 @@ class UsecaseShowJsonRenderer
         return (int)($row['uid'] ?? 0);
     }
 
-    /** Resolve a page uid to its frontend path (route enhancer aware). */
+    /**
+     * Resolve a page uid to its frontend path (route enhancer aware).
+     *
+     * Callers here build paths by concatenation, so the empty string stays the
+     * "no link" value; LinkResolver's null is coalesced away.
+     */
     private function resolvePageUrl(int $pageUid): string
     {
-        try {
-            $cObj = GeneralUtility::makeInstance(\TYPO3\CMS\Frontend\ContentObject\ContentObjectRenderer::class);
-            return (string)$cObj->typoLink_URL(['parameter' => (string)$pageUid]);
-        } catch (\Throwable $e) {
-            return '';
-        }
+        return LinkResolver::pageUrl($pageUid) ?? '';
     }
 }