feat(korrespondenz): address PR #164 review – blockers and suggestions

Blockers (14):
- B1: fix senderName/receiverName to use $derived instead of $state + sync $effect
- B2: migrate all korrespondenz components from messages-extra shim to paraglide m.*
- B3: i18n CorrespondenzEmptyState (heading, subtext, search placeholder)
- B4: add response.ok checks to admin layout server load
- B5: add response.ok checks to korrespondenz page server load
- B6: add page.server.spec.ts with 5 test suites for korrespondenz load function
- B7: add axe-core accessibility checks to all e2e korrespondenz tests
- B8: add Testcontainers JPQL tests for findSinglePersonCorrespondence (DISTINCT + sender)
- B9: hide auth reset-token endpoint from OpenAPI spec; remove from generated api.ts
- B11: replace amber hardcoded hex colors in SinglePersonHintBar with brand tokens
- B12: replace clipboard emoji with Heroicons SVG in SinglePersonHintBar
- B13: create DateInput component (German dd.mm.yyyy); use it in CorrespondenzFilterControls
- B14: add Paraglide compile step to CI workflow before lint/test

Suggestions (11):
- S1: make CorrespondentSuggestionsDropdown a pure display component; lift fetch to PersonBar
- S2: fix leftover messages-extra import in ConversationTimeline; use brand tokens for status dots
- S3: add intent comment to EntityNav openFlyout behavior
- S4: rename canManageGroups → canManagePermissions throughout admin
- S6: remove domFlush helper from DateInput spec; use expect.poll instead
- S7: replace test.skip with throw new Error in bilateral e2e tests
- S8: add inverse aria-disabled test for filter strip
- S9: remove sm:min-h-0 from sort button to preserve 44px touch target
- S10: add title attributes to tablet trigger buttons in EntityNav
- S11: delete messages-extra.ts shim entirely

Also: fix admin pages revealing blank strip at bottom (-mb-6 on admin layout)

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

frontend/src/routes/korrespondenz/+page.svelte

@@ -11,25 +11,21 @@ import { m } from '$lib/paraglide/messages.js';
 
 let { data } = $props();
 
+// Filter values are local $state so swapPersons/toggleSort can mutate them before goto.
+// They are initialised once from server data and never re-synced — navigation replaces
+// the page component, so each load gets a fresh init.
 let senderId = $state(untrack(() => data.filters.senderId));
 let receiverId = $state(untrack(() => data.filters.receiverId));
 let fromDate = $state(untrack(() => data.filters.from));
 let toDate = $state(untrack(() => data.filters.to));
 let sortDir = $state(untrack(() => data.filters.dir));
 
-// Derived name states — kept as reactive copies so ConversationTimeline always has current names
-let senderName = $state(untrack(() => data.initialValues.senderName));
-let receiverName = $state(untrack(() => data.initialValues.receiverName));
+// Names are pure reads of server data — no local mutation needed.
+const senderName = $derived(data.initialValues.senderName);
+const receiverName = $derived(data.initialValues.receiverName);
 
-// Sync with server data after navigation; persist recent persons once the name is resolved
+// Side-effect only: persist the resolved sender to localStorage once the name is available.
 $effect(() => {
-	senderId = data.filters.senderId;
-	receiverId = data.filters.receiverId;
-	fromDate = data.filters.from;
-	toDate = data.filters.to;
-	sortDir = data.filters.dir;
-	senderName = data.initialValues.senderName;
-	receiverName = data.initialValues.receiverName;
 	if (data.filters.senderId && data.initialValues.senderName) {
 		persistRecentPerson(data.filters.senderId, data.initialValues.senderName);
 	}