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.

resources/views/admin.phtml

@@ -47,6 +47,7 @@ use Illuminate\Support\Collection;
             $annivs    = Configuration::includeAnniversaries($tree);
             $subject   = Configuration::subjectPrefix($tree);
             $extras    = $tree->getPreference(Configuration::PREF_EXTRA_RECIPIENTS, '');
+            $lineal    = Configuration::linealDepth($tree);
             $last_sent = Configuration::lastSentAt($tree);
         ?>
 
@@ -129,6 +130,22 @@ use Illuminate\Support\Collection;
                     </div>
                 </div>
 
+                <div class="row mb-3">
+                    <label class="col-sm-3 col-form-label" for="lineal-<?= $id ?>">
+                        <?= I18N::translate('Detailed view depth (generations)') ?>
+                    </label>
+                    <div class="col-sm-9">
+                        <input class="form-control" type="number" style="max-width: 18rem;"
+                               id="lineal-<?= $id ?>" name="lineal-<?= $id ?>"
+                               value="<?= e((string) $lineal) ?>"
+                               min="<?= Configuration::MIN_LINEAL_DEPTH ?>"
+                               max="<?= Configuration::MAX_LINEAL_DEPTH ?>" required>
+                        <small class="form-text text-muted">
+                            <?= I18N::translate('Recipients see profile pictures, icons and the timeline only for their own direct ancestors and descendants within this many generations. Everyone else appears as a compact text list at the bottom of each section. Set to 0 to render the whole newsletter as text. Recipients with no linked tree record always see the full detailed view.') ?>
+                        </small>
+                    </div>
+                </div>
+
                 <div class="row mb-3">
                     <label class="col-sm-3 col-form-label" for="subject-<?= $id ?>">
                         <?= I18N::translate('Subject prefix') ?>