fix(ux): human-readable API errors instead of raw api_error_NNN codes

apiFetch threw new Error(api_error_<status>), so any UI fallback to (e).message showed a cryptic code, and some flows surfaced bare codes like slug_taken. Added a central humanizeError() in lib/api.ts: prefers the backend detail sentence, then a mapped friendly message per known code, then a status-based fallback - never a raw code. apiFetch now sets the thrown error message via it, so every (e).message fallback across the app becomes a real sentence. Wizard analyze/build now use humanizeError directly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -5,7 +5,7 @@ import { Input, Label, Textarea } from '@/components/input';
 import { InstallSnippets } from '@/components/install-snippets';
 import { StreamingLogs } from '@/components/streaming-logs';
 import { Button } from '@/components/ui/button';
-import { apiFetch, apiSseStream } from '@/lib/api';
+import { apiFetch, apiSseStream, humanizeError } from '@/lib/api';
 import { findSecretInPrompt } from '@bmm/types';
 import { Loader2, RotateCcw, X } from 'lucide-react';
 import Link from 'next/link';
@@ -302,8 +302,7 @@ function NewServerPageInner() {
         setStep('confirm');
         return;
       } catch (e) {
-        const detail = (e as { detail?: { error?: string; detail?: string } }).detail;
-        setError(detail?.detail ?? detail?.error ?? (e as Error).message);
+        setError(humanizeError(e));
         setStep('prompt');
         return;
       }
@@ -458,7 +457,7 @@ function NewServerPageInner() {
         setError(detail?.detail ?? 'Daily build limit reached — try again tomorrow or upgrade.');
         return;
       }
-      setError(detail?.detail ?? code ?? (e as Error).message);
+      setError(humanizeError(e));
     }
   }