fix(wizard): fork 409 — auto-unique slug + editable name/slug in fork step

Bug: forking a template POSTed /v1/servers with slug = trySlug(template.title),
a fixed value. If the user had any server with that slug already (e.g. forking
the same template twice, or a name collision), the create returned 409
slug_taken — and the fork wizard skips Step 1, so there was no slug field to
fix it with. The user was stuck (8 repeated 409s in the report).

Fix:
- On fork setup, after the fork call, GET /v1/servers and auto-unique the
  default slug: echo-demo-template -> echo-demo-template-2 -> -3 ... against the
  user's existing slugs. Lookup failure is non-fatal (slug field is editable).
- Fork step 2 now renders editable Name + Slug fields in the fork banner
  ('must be unique in your workspace' hint) — the normal wizard has these in
  Step 1, which the fork flow skips, so they belong here.
- slug_taken build error now reads 'The slug "x" is already used by one of
  your servers — change the Slug field above' instead of the raw code.

Note: the SES lockdown-install.js and content.js 'query' errors in the report
are browser extensions, not the app.

Verified: forked echo-demo-template (whose base slug was already taken) — slug
auto-filled echo-demo-template-2, build succeeded, container live on :4111,
template fork_count incremented to 2.

apps/web/app/(dashboard)/servers/new/page.tsx

@@ -130,8 +130,27 @@ export default function NewServerPage() {
           };
         }>(`/v1/templates/${templateSlug}/fork`, { method: 'POST', body: '{}' });
         if (cancelled) return;
+
+        // Auto-unique the slug against the user's existing servers so the
+        // default fork doesn't 409 (e.g. forking the same template twice).
+        let uniqueSlug = trySlug(res.template.title);
+        try {
+          const own = await apiFetch<{ servers: { slug: string }[] }>('/v1/servers');
+          const taken = new Set(own.servers.map((s) => s.slug));
+          if (taken.has(uniqueSlug)) {
+            const base = uniqueSlug;
+            let n = 2;
+            while (taken.has(`${base}-${n}`)) n++;
+            uniqueSlug = `${base}-${n}`;
+          }
+        } catch {
+          // If the lookup fails we still proceed; the slug field is editable
+          // and the build surfaces a clear slug_taken error.
+        }
+        if (cancelled) return;
+
         setName(res.template.title);
-        setSlug(trySlug(res.template.title));
+        setSlug(uniqueSlug);
         setPrompt(`Fork of "${res.template.title}" template.`);
         setForkedTemplateId(res.templateId);
         setForkedTemplateTitle(res.template.title);
@@ -325,7 +344,12 @@ export default function NewServerPage() {
       setStep('building');
     } catch (e) {
       const detail = (e as { detail?: { error?: string; detail?: unknown } }).detail;
-      setError(detail?.error ?? (e as Error).message);
+      const code = detail?.error;
+      setError(
+        code === 'slug_taken'
+          ? `The slug "${slug}" is already used by one of your servers — change the Slug field above.`
+          : (code ?? (e as Error).message),
+      );
     }
   }
 
@@ -424,19 +448,44 @@ export default function NewServerPage() {
       {step === 'confirm' && preview && editable && (
         <div className="mt-7 space-y-6">
           {forkedTemplateTitle && (
-            <div className="panel-subtle p-3 flex items-center justify-between">
+            <div className="panel-subtle p-3 space-y-3">
-              <div className="text-[12.5px]">
+              <div className="flex items-center justify-between">
-                Forking <span className="mono font-semibold">{forkedTemplateTitle}</span> — fill in
+                <div className="text-[12.5px]">
-                your own credentials below. The template author never sees them.
+                  Forking <span className="mono font-semibold">{forkedTemplateTitle}</span> — name
+                  your copy and fill in your own credentials. The template author never sees them.
+                </div>
+                <a
+                  href={`/templates/${templateSlug}`}
+                  target="_blank"
+                  rel="noreferrer"
+                  className="shrink-0 text-[11.5px] text-[--color-fg-muted] underline hover:text-[--color-fg]"
+                >
+                  Template ↗
+                </a>
+              </div>
+              <div className="grid gap-3 md:grid-cols-2">
+                <div className="space-y-1.5">
+                  <Label htmlFor="fork-name">Name</Label>
+                  <Input
+                    id="fork-name"
+                    value={name}
+                    onChange={(e) => {
+                      setName(e.target.value);
+                      if (!slug || slug === trySlug(name)) setSlug(trySlug(e.target.value));
+                    }}
+                  />
+                </div>
+                <div className="space-y-1.5">
+                  <Label htmlFor="fork-slug" hint="must be unique in your workspace">
+                    Slug
+                  </Label>
+                  <Input
+                    id="fork-slug"
+                    value={slug}
+                    onChange={(e) => setSlug(trySlug(e.target.value))}
+                  />
+                </div>
               </div>
-              <a
-                href={`/templates/${templateSlug}`}
-                target="_blank"
-                rel="noreferrer"
-                className="text-[11.5px] text-[--color-fg-muted] underline hover:text-[--color-fg]"
-              >
-                Template ↗
-              </a>
             </div>
           )}
           <div className="panel p-4">