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/routes/geschichten/new/JourneyCreate.svelte

@@ -61,6 +61,7 @@ async function handleSubmit(e: SubmitEvent) {
 		<input
 			type="text"
 			bind:value={title}
+			maxlength="255"
 			onblur={() => (titleTouched = true)}
 			placeholder={m.geschichte_editor_title_placeholder()}
 			aria-label={m.journey_title_aria_label()}
@@ -78,7 +79,7 @@ async function handleSubmit(e: SubmitEvent) {
 		<button
 			type="submit"
 			disabled={submitting}
-			class="inline-flex h-11 items-center rounded bg-brand-navy px-4 font-sans text-sm font-medium text-white hover:opacity-90 focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring disabled:opacity-50"
+			class="inline-flex h-11 items-center rounded bg-primary px-4 font-sans text-sm font-medium text-primary-fg hover:opacity-90 focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring disabled:opacity-50"
 		>
 			{m.journey_create_submit()}
 		</button>