fix(geschichten): widen story body and lift section-header contrast

Story-detail body now uses an explicit Tailwind block-element selector
ruleset instead of the `prose` plugin, so the body fills the full max-w-3xl
parent width — previously `prose` clamped to ~65ch inside an already narrow
page.

GeschichtenCard heading and the "+ Geschichte schreiben" link now use
text-ink-2 (#4b5563 = 7.6:1 on white, AAA-passable) instead of text-ink-3
or text-ink/60. Same fix on the "+ Geschichte anhängen" link in the
Document drawer column and on the Personen / Dokumente section headers
on the story detail page.

Closes Leonie's review B1, B2 and S4 on PR #382.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/components/DocumentMetadataDrawer.svelte

@@ -199,7 +199,7 @@ function getFullName(person: Person): string {
 					{#if canBlogWrite && documentId}
 						<a
 							href="/geschichten/new?documentId={documentId}"
-							class="font-sans text-xs font-medium text-ink/60 hover:text-ink"
+							class="font-sans text-xs font-medium text-ink-2 hover:text-ink"
 						>
 							{m.geschichten_card_attach_action()}
 						</a>

frontend/src/lib/components/GeschichtenCard.svelte

@@ -39,14 +39,14 @@ function authorName(g: Geschichte): string {
 		<header class="mb-5 flex items-center justify-between">
 			<h2
 				id="geschichten-card-heading"
-				class="font-sans text-xs font-bold tracking-widest text-ink-3 uppercase"
+				class="font-sans text-xs font-bold tracking-widest text-ink-2 uppercase"
 			>
 				{m.geschichten_card_heading()}
 			</h2>
 			{#if canWrite}
 				<a
 					href="/geschichten/new?personId={personId}"
-					class="inline-flex items-center font-sans text-sm font-medium text-ink/60 hover:text-ink"
+					class="inline-flex items-center font-sans text-sm font-medium text-ink-2 hover:text-ink"
 				>
 					{m.geschichten_card_write_action()}
 				</a>