fix(picker): honest combobox — keyboard navigation, listbox roles, no-results state

The input declared role=combobox + aria-autocomplete=list while arrow keys
did nothing (WCAG 4.1.2). Wired the useTypeahead activeIndex the same way
PersonTypeahead does: ArrowUp/Down cycle, Enter/Space select, Escape closes,
aria-activedescendant tracks the active option; the list is a real listbox
with option roles again (the interim role downgrade is reverted). Zero hits
now render a 'Keine Treffer' row instead of silently vanishing, aria-expanded
matches the visible state, and the hook sets loading at setQuery so the
debounce window can't read as 'no results'. DocumentMultiSelect renders the
shared error state too. _uid counter replaced with $props.id().

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

frontend/messages/en.json

@@ -302,6 +302,7 @@
 	"comp_multiselect_remove": "Remove",
 	"comp_multiselect_loading": "Searching...",
 	"comp_typeahead_error": "Search failed. Please try again.",
+	"comp_typeahead_no_results": "No matches",
 	"comp_taginput_placeholder_create": "Add tags...",
 	"comp_taginput_placeholder_filter": "Filter by tags...",
 	"comp_taginput_remove": "Remove tag",
@@ -1179,6 +1180,11 @@
 	"journey_selector_aria_live_hint": "Please select a type to continue.",
 	"journey_add_document": "Add letter",
 	"journey_add_interlude": "Add interlude",
+	"journey_interlude_label": "Interlude",
+	"journey_item_pending_remove": "removing…",
+	"journey_publish_disabled_hint": "A title and at least one entry are required.",
+	"journey_title_aria_label": "Title of the reading journey",
+	"journey_intro_aria_label": "Introduction of the reading journey",
 	"journey_note_add": "Add note",
 	"journey_note_remove": "Remove note",
 	"journey_note_save_hint": "Saved when you leave the field.",