ui: chat compose grows with content + better default size

- rows='1' → rows='3' so the compose box has presence even when empty
  (it was a one-line slit, easy to miss).
- Add `field-sizing: content` on .fb-compose__textarea so modern browsers
  (Chrome 123+ / Firefox 137+ / Safari 17.4+) auto-grow it to fit content
  natively. Cap at the existing max-height: 10rem with overflow-y: auto so
  long messages don't eat the bubbles scroll area.
- For older browsers: feature-detect via CSS.supports('field-sizing',
  'content'). When unsupported, an oninput handler sets style.height =
  scrollHeight + 'px' (capped at 160px). Modern browsers no-op the JS
  resizer to avoid fighting the native CSS rule.
- After send (chatBody → ''), an $effect clears the inline height so the
  textarea snaps back to rows='3'. Native field-sizing handles this on
  its own; the effect only fires on the JS-fallback path.
- Shorten placeholder to "Nachricht…" — the keyboard hint was chrome the
  user discovers on their own.

src/lib/styles/feedback.css

@@ -1835,6 +1835,11 @@ body { min-height: 100vh; }
 	min-height: 2.5rem;
 	max-height: 10rem;
 	resize: none;
+	overflow-y: auto;
+	/* Modern browsers (Chrome 123+ / Firefox 137+ / Safari 17.4+) auto-grow
+	   the textarea to fit its content. Older browsers fall back to the JS
+	   resizer in /f/[slug]/+page.svelte's autosizeCompose. */
+	field-sizing: content;
 }
 
 .fb-compose__send {

src/routes/f/[slug]/+page.svelte

@@ -56,6 +56,7 @@
 	let pollHandle: ReturnType<typeof setInterval> | null = null;
 	let lastSeenAt: string | null = null;
 	let chatListEl = $state<HTMLDivElement | null>(null);
+	let composeEl = $state<HTMLTextAreaElement | null>(null);
 
 	let results = $state<AggregatedResults | null>(null);
 	let resultsPollHandle: ReturnType<typeof setInterval> | null = null;
@@ -436,6 +437,28 @@
 		}
 	}
 
+	// Auto-grow the compose textarea with content. Modern browsers handle this
+	// natively via `field-sizing: content`; for older browsers we fall back to
+	// resizing on input. Capped at 10rem (160px) — matches .fb-compose__textarea.
+	const supportsFieldSizing =
+		typeof CSS !== 'undefined' && typeof CSS.supports === 'function'
+			? CSS.supports('field-sizing', 'content')
+			: false;
+
+	function autosizeCompose(el: HTMLTextAreaElement): void {
+		if (supportsFieldSizing) return;
+		el.style.height = 'auto';
+		el.style.height = `${Math.min(el.scrollHeight, 160)}px`;
+	}
+
+	// Reset the inline height after a send (chatBody → '') so the textarea
+	// snaps back to its rows="3" default. No-op when field-sizing handles it.
+	$effect(() => {
+		if (chatBody === '' && composeEl && !supportsFieldSizing) {
+			composeEl.style.height = '';
+		}
+	});
+
 	function onComposeKeydown(e: KeyboardEvent): void {
 		// Enter alone (no shift, no IME composition) sends. Shift+Enter inserts a newline.
 		// Cmd/Ctrl+Enter also sends — covers users who expect that shortcut.
@@ -800,11 +823,13 @@
 					>
 						<textarea
 							class="fb-textarea fb-compose__textarea"
-							placeholder="Dein Beitrag … (Enter zum Senden, Shift+Enter für Zeilenumbruch)"
+							placeholder="Nachricht…"
 							maxlength="2000"
 							bind:value={chatBody}
+							bind:this={composeEl}
 							onkeydown={onComposeKeydown}
-							rows="1"
+							oninput={(e) => autosizeCompose(e.currentTarget as HTMLTextAreaElement)}
+							rows="3"
 						></textarea>
 						<button
 							type="submit"