Limit detailed view to lineal kin; rest as summary bullets

Per-recipient: only direct ancestors and direct descendants
within a configurable number of generations (default 3) get the
full row treatment (avatar, icon, timeline). Everyone else falls
through to a compact text-only bullet list at the bottom of the
same section.

- New tree preference NEWSLETTER_LINEAL_DEPTH (range 0–10,
  default 3) with a clearly-explained admin input.
- RelationshipPathFinder::linealKin() does two cheap recursive
  expansions (ancestors and descendants only — no spouse or
  sibling traversal) and returns the xref set. Memoised per
  recipient within a dispatch run.
- Avatar attachments are filtered per recipient to only the
  embeds actually referenced in their HTML, so summary-only rows
  no longer inflate per-email size with unused images.
- Recipients with no PREF_TREE_ACCOUNT_XREF (external admin
  addresses, users not linked to a record) see the entire
  newsletter in detail — no lineal anchor to filter against.
- German translations for the three new section kickers ("Other
  birthdays", etc.) and the admin input help text.

src/Services/RelationshipPathFinder.php

@@ -33,6 +33,9 @@ final class RelationshipPathFinder
     /** Default BFS depth — ~7 generations of ancestry / descent. */
     public const int DEFAULT_MAX_DEPTH = 14;
 
+    /** @var array<string,array<string,true>> Cache: xref => {ancestor/descendant xref set} */
+    private array $lineal_cache = [];
+
     /** @var array<string,string|null> Cache: "fromXref|toXref" -> label */
     private array $label_cache = [];
 
@@ -74,6 +77,77 @@ final class RelationshipPathFinder
         return $this->label_cache[$cache_key] = $this->relationship_service->nameFromPath($path, $language);
     }
 
+    /**
+     * Set of xrefs that are direct ancestors or direct descendants of
+     * `$root` within `$depth` generations.
+     *
+     * Only lineal hops are followed (parent ↔ child) — spouses,
+     * siblings, and step-relations are deliberately excluded. The
+     * recipient's own xref is included in the set.
+     *
+     * The result is memoised: callers may invoke this once per
+     * recipient and reuse it across all featured xrefs.
+     *
+     * @return array<string,true>
+     */
+    public function linealKin(Individual $root, int $depth): array
+    {
+        if ($depth < 0) {
+            return [$root->xref() => true];
+        }
+
+        $cache_key = $root->xref() . '|' . $depth;
+
+        if (isset($this->lineal_cache[$cache_key])) {
+            return $this->lineal_cache[$cache_key];
+        }
+
+        $set = [$root->xref() => true];
+
+        $this->expandAncestors($root, $depth, $set);
+        $this->expandDescendants($root, $depth, $set);
+
+        return $this->lineal_cache[$cache_key] = $set;
+    }
+
+    /**
+     * @param array<string,true> $set
+     */
+    private function expandAncestors(Individual $indi, int $depth, array &$set): void
+    {
+        if ($depth <= 0) {
+            return;
+        }
+
+        foreach ($indi->childFamilies(Auth::PRIV_HIDE) as $family) {
+            foreach ($family->spouses(Auth::PRIV_HIDE) as $parent) {
+                if (!isset($set[$parent->xref()])) {
+                    $set[$parent->xref()] = true;
+                    $this->expandAncestors($parent, $depth - 1, $set);
+                }
+            }
+        }
+    }
+
+    /**
+     * @param array<string,true> $set
+     */
+    private function expandDescendants(Individual $indi, int $depth, array &$set): void
+    {
+        if ($depth <= 0) {
+            return;
+        }
+
+        foreach ($indi->spouseFamilies(Auth::PRIV_HIDE) as $family) {
+            foreach ($family->children(Auth::PRIV_HIDE) as $child) {
+                if (!isset($set[$child->xref()])) {
+                    $set[$child->xref()] = true;
+                    $this->expandDescendants($child, $depth - 1, $set);
+                }
+            }
+        }
+    }
+
     /**
      * BFS over child- and spouse-families, exactly matching
      * RelationshipService::getCloseRelationship's traversal but with