Integrate Vantage live map for guild claims [skip ci]

panel/web/src/components/ServerForm.svelte

@@ -18,6 +18,7 @@
 
 <label class="field">Name<input bind:value={draft.name} maxlength="48" placeholder="Survival SMP" /></label>
 <label class="field">Launcher instance<select bind:value={draft.instance_id}><option value="">Unlinked</option>{#each instances as instance}<option value={instance.id}>{instance.name}</option>{/each}</select></label>
+<label class="field">Vantage live map manifest URL<input type="url" bind:value={draft.map_url} placeholder="https://maps.example.com/world.json" /><span class="tiny muted">Optional. Use a public Vantage render or a session-gated same-origin endpoint. The URL is visible to launcher users.</span></label>
 <div class="field">
   <span class="lbl">Who can join</span>
   <div class="opts">