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/GeschichteListRow.svelte.spec.ts

@@ -79,12 +79,12 @@ describe('GeschichteListRow', () => {
 		expect(badge?.tagName.toLowerCase()).toBe('span');
 	});
 
-	it('badge has small font size appropriate for a label', async () => {
+	it('badge uses the 12px label size — text-xs is the visible-text floor', async () => {
 		render(GeschichteListRow, { props: { geschichte: baseRow({ type: 'JOURNEY' }) } });
 		const badge = document.querySelector('[data-testid="journey-badge"]');
-		const fontSize = parseFloat(window.getComputedStyle(badge!).fontSize);
-		expect(fontSize).toBeGreaterThan(0);
-		expect(fontSize).toBeLessThanOrEqual(14); // label badge must not exceed body text size
+		expect(badge!.className).toContain('text-xs');
+		// 10px was below the house floor for the 60+ audience (round-3 review)
+		expect(badge!.className).not.toContain('text-[10px]');
 	});
 
 	it('renders author name in meta line', async () => {