mAi: #2 - admin Share section + env-var docs

Self-contained "Share" section on the admin detail page. When no short URL
exists yet: shows an optional custom-slug input + "Create short link"
button. When one exists: shows the URL with Copy + Open buttons and a
collapsed "Replace" form for picking a new slug.

Append-only — does not touch existing buttons, the icon system, or
feedback.css; uses inline styles + existing fb-* classes only, so it stays
out of dokploy's parallel button-system refactor.

.env.example documents SHLINK_URL + SHLINK_API_KEY (must be copied from the
flexsiebels.de Dokploy app config to fdbck.msbls.de before this works in
prod).

Refs m/fdbck#2.

.env.example

@@ -10,3 +10,8 @@ PUBLIC_SITE_URL=https://fdbck.msbls.de
 
 # Optional cookie scope (leave unset for host-only)
 # COOKIE_DOMAIN=.msbls.de
+
+# Shlink short-URL service (admin "Share" feature)
+# SHLINK_URL defaults to https://msbls.de when unset.
+SHLINK_URL=https://msbls.de
+SHLINK_API_KEY=

src/routes/admin/feedback/[id]/+page.svelte

@@ -24,6 +24,11 @@
 	let editChatEnabled = $state(inst.chat_enabled);
 	let editLiveResults = $state(inst.live_results_enabled);
 
+	let shareSlugInput = $state('');
+	let shareInFlight = $state(false);
+	let shareError = $state<string | null>(null);
+	let shareCopied = $state(false);
+
 	let editMode = $state<'visual' | 'json'>('visual');
 	let editForm = $state<FeedbackFormDefinition | null>(
 		inst.form_definition ? (inst.form_definition as FeedbackFormDefinition) : null,
@@ -213,6 +218,46 @@
 		}
 	}
 
+	async function copyShortUrl(): Promise<void> {
+		if (!inst.short_url) return;
+		try {
+			await navigator.clipboard.writeText(inst.short_url);
+			shareCopied = true;
+			setTimeout(() => (shareCopied = false), 1500);
+		} catch {
+			// silent
+		}
+	}
+
+	async function createShareLink(): Promise<void> {
+		shareError = null;
+		shareInFlight = true;
+		try {
+			const slug = shareSlugInput.trim();
+			const body: { customSlug?: string } = {};
+			if (slug) body.customSlug = slug;
+
+			const res = await fetch(`/api/admin/feedback/${inst.id}/share`, {
+				method: 'POST',
+				headers: { 'Content-Type': 'application/json' },
+				body: JSON.stringify(body),
+			});
+			if (!res.ok) {
+				const j = (await res.json().catch(() => ({}))) as { error?: string; details?: unknown };
+				shareError = j.error ?? `Error ${res.status}`;
+				if (j.details) shareError += ' — ' + JSON.stringify(j.details);
+				return;
+			}
+			const j = (await res.json()) as { instance: typeof inst };
+			inst = j.instance;
+			shareSlugInput = '';
+		} catch (e) {
+			shareError = e instanceof Error ? e.message : 'Network error';
+		} finally {
+			shareInFlight = false;
+		}
+	}
+
 	function fmtDateTime(iso: string): string {
 		return new Date(iso).toLocaleString();
 	}
@@ -288,6 +333,91 @@
 		<div class="fb-banner fb-banner--error">{actionError}</div>
 	{/if}
 
+	<section class="fb-section" data-fb-share>
+		<h2>Share</h2>
+		{#if inst.short_url}
+			<p style="margin: 0 0 0.5rem 0; color: var(--color-text-muted); font-size: 0.85rem;">
+				Memorable short link — resolves to <code>/f/{inst.slug}</code>.
+			</p>
+			<div style="display: flex; gap: 0.5rem; flex-wrap: wrap; align-items: center;">
+				<a
+					href={inst.short_url}
+					target="_blank"
+					rel="noopener"
+					style="font-family: ui-monospace, 'SF Mono', Menlo, monospace; font-size: 0.95rem; word-break: break-all;"
+				>
+					{inst.short_url}
+				</a>
+				<button type="button" class="fb-btn fb-btn--ghost" onclick={copyShortUrl}>
+					{shareCopied ? 'Copied' : 'Copy'}
+				</button>
+				<a class="fb-btn fb-btn--ghost" href={inst.short_url} target="_blank" rel="noopener">
+					Open ↗
+				</a>
+			</div>
+			<details style="margin-top: 0.75rem;">
+				<summary style="cursor: pointer; color: var(--color-text-muted); font-size: 0.85rem;">
+					Replace with a different short link
+				</summary>
+				<div style="margin-top: 0.5rem;">
+					<label class="fb-question__label" for="fb-share-slug-replace">Custom slug (optional)</label>
+					<div style="display: flex; gap: 0.5rem; flex-wrap: wrap; align-items: center;">
+						<input
+							id="fb-share-slug-replace"
+							class="fb-input"
+							maxlength="64"
+							placeholder="e.g. vote, session-feedback"
+							bind:value={shareSlugInput}
+							style="max-width: 320px;"
+						/>
+						<button
+							type="button"
+							class="fb-btn"
+							disabled={shareInFlight}
+							onclick={createShareLink}
+						>
+							{shareInFlight ? 'Creating…' : 'Create new'}
+						</button>
+					</div>
+					<p style="margin: 0.4rem 0 0 0; color: var(--color-text-muted); font-size: 0.8rem;">
+						Leave blank for a random short code, or pick a memorable slug like <code>vote</code> or <code>session-feedback</code>.
+					</p>
+				</div>
+			</details>
+		{:else}
+			<p style="margin: 0 0 0.5rem 0; color: var(--color-text-muted); font-size: 0.85rem;">
+				Create a memorable short link (e.g. <code>https://msbls.de/vote</code>) that redirects to this form.
+			</p>
+			<div style="margin-top: 0.5rem;">
+				<label class="fb-question__label" for="fb-share-slug">Custom slug (optional)</label>
+				<div style="display: flex; gap: 0.5rem; flex-wrap: wrap; align-items: center;">
+					<input
+						id="fb-share-slug"
+						class="fb-input"
+						maxlength="64"
+						placeholder="e.g. vote, session-feedback"
+						bind:value={shareSlugInput}
+						style="max-width: 320px;"
+					/>
+					<button
+						type="button"
+						class="fb-btn"
+						disabled={shareInFlight}
+						onclick={createShareLink}
+					>
+						{shareInFlight ? 'Creating…' : 'Create short link'}
+					</button>
+				</div>
+				<p style="margin: 0.4rem 0 0 0; color: var(--color-text-muted); font-size: 0.8rem;">
+					Leave blank for a random short code, or pick a memorable slug like <code>vote</code> or <code>session-feedback</code>.
+				</p>
+			</div>
+		{/if}
+		{#if shareError}
+			<div class="fb-banner fb-banner--error" style="margin-top: 0.5rem;">{shareError}</div>
+		{/if}
+	</section>
+
 	<div class="fb-tabs">
 		{#each [
 			{ key: 'chat', label: `Chat (${posts.length})`, show: inst.chat_enabled },