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/ModelcardJsonRenderer.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\RteResolver;
 use Evomedien\Vitec\Service\UsecaseSerializer;
 use TYPO3\CMS\Core\Attribute\AsAllowedCallable;
@@ -163,7 +164,7 @@ class ModelcardJsonRenderer
             ];
         }
 
-        // market | solution — identical field set.
+        // market | solution — identical field set, both carry `detail_page`.
         return [
             'uid' => $uid,
             'title' => (string)($row['title'] ?? ''),
@@ -171,6 +172,7 @@ class ModelcardJsonRenderer
             'subtitle' => (string)($row['subtitle'] ?? ''),
             'teaser' => (string)($row['teaser'] ?? ''),
             'description' => RteResolver::html($row['description'] ?? ''),
+            'detailUrl' => LinkResolver::pageUrl((int)($row['detail_page'] ?? 0)),
             'image' => $serializer->image($uid, 'image', self::MODEL_TABLES[$modelType], true),
         ];
     }