fix(geschichte-ui): a11y and visual round-3 batch

- JourneyItemCard: 'Brief öffnen' back to a >=44px touch target with the
  height regression spec restored
- GeschichteListRow: REISE badges text-[10px] -> text-xs; drop the
  hardcoded aria-label and the mobile badge's aria-hidden so phone screen
  readers learn a row is a Lesereise; mobile avatar initials -> color dot
- detail page: badge text-xs, metabar Edit/Delete h-9 -> h-11, avatar
  color keyed by name to match the list
- JourneyReader: dead border-subtle class -> border-line-2
- DocumentPickerDropdown: aria-controls only while the listbox exists
- JourneyAddBar: aria-expanded/aria-controls on both toggles + focus
  hand-off into the revealed picker input / interlude textarea
- GeschichteSidebar: section h2s hidden below sm (summary already shows
  the label there)
- JourneyCreate: bg-brand-navy -> semantic bg-primary/text-primary-fg;
  title maxlength=255
- JourneyItemRow interlude: neutral frame border + left accent only,
  token utilities instead of arbitrary var() syntax and inline style

Review round 3: Leonie (1-8 + round-1 leftovers), Elicit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/lib/geschichte/GeschichteSidebar.svelte

@@ -22,7 +22,10 @@ const isDraft = $derived(status === 'DRAFT');
 			{m.geschichte_sidebar_status()}
 		</summary>
 		<section class="rounded border border-line bg-surface p-4 shadow-sm">
-			<h2 class="mb-1 font-sans text-xs font-bold tracking-widest text-ink-3 uppercase">
+			<!-- hidden below sm: the <summary> already shows this label there -->
+			<h2
+				class="mb-1 hidden font-sans text-xs font-bold tracking-widest text-ink-3 uppercase sm:block"
+			>
 				{m.geschichte_sidebar_status()}
 			</h2>
 			<p class="mb-3">
@@ -50,7 +53,9 @@ const isDraft = $derived(status === 'DRAFT');
 			{m.geschichte_editor_personen_heading()}
 		</summary>
 		<section class="rounded border border-line bg-surface p-4 shadow-sm">
-			<h2 class="mb-2 font-sans text-xs font-bold tracking-widest text-ink-3 uppercase">
+			<h2
+				class="mb-2 hidden font-sans text-xs font-bold tracking-widest text-ink-3 uppercase sm:block"
+			>
 				{m.geschichte_editor_personen_heading()}
 			</h2>
 			<p class="mb-3 font-sans text-xs text-ink-3">{m.geschichte_editor_personen_hint()}</p>