fix(korrespondenz): address 10 visual and functional regressions

- Strip full-bleed: remove max-w container, put strips at page level
- Remove page heading/subtitle above strip (not in spec)
- Swap button always visible (drop opacity-0, keep pointer-events-none)
- Korrespondent placeholder "Alle Korrespondenten" + label "— optional"
- Add placeholder prop to PersonTypeahead; add onfocused callback prop
- "Person suchen" button now focuses #senderId-search instead of no-op navigate
- Wire CorrespondentSuggestionsDropdown on correspondent field focus
- Hint bar: bold name via <strong>, year-only dates (no ISO strings)
- Asymmetry bar: use first name only to prevent label overflow

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/PersonTypeahead.svelte

@@ -10,8 +10,10 @@ interface Props {
 	value?: string;
 	initialName?: string;
 	suggestedName?: string;
+	placeholder?: string;
 	restrictToCorrespondentsOf?: string;
 	onchange?: (value: string) => void;
+	onfocused?: () => void;
 }
 
 let {
@@ -20,8 +22,10 @@ let {
 	value = $bindable(''),
 	initialName = '',
 	suggestedName = '',
+	placeholder,
 	restrictToCorrespondentsOf,
-	onchange
+	onchange,
+	onfocused
 }: Props = $props();
 
 let searchTerm = $state(initialName);
@@ -79,6 +83,7 @@ function handleInput() {
 }
 
 function handleFocus() {
+	onfocused?.();
 	showDropdown = true;
 	if (restrictToCorrespondentsOf) {
 		const personId = untrack(() => restrictToCorrespondentsOf)!;
@@ -131,7 +136,7 @@ function clickOutside(node: HTMLElement) {
 		bind:value={searchTerm}
 		oninput={handleInput}
 		onfocus={handleFocus}
-		placeholder={m.comp_typeahead_placeholder()}
+		placeholder={placeholder ?? m.comp_typeahead_placeholder()}
 		class="mt-1 block w-full rounded-md border border-line p-2 shadow-sm focus:border-accent focus:ring-accent"
 	/>