feat(navi): config-driven tile source, defaults, and feature flags

Load deployment config from /api/config on startup:
- src/config.js: loader with 3s timeout + hardcoded fallback
- src/hooks/useConfig.js: useConfig() and useFeature() hooks
- MapView.jsx: tile URL, attribution, center, zoom from config
- main.jsx: loads config before first render

Falls back to home profile defaults if backend unavailable.
No visible behavior change — infrastructure for future features.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main.jsx

@@ -1,23 +1,27 @@
 import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 import { Toaster } from 'react-hot-toast'
+import { loadConfig } from './config'
 import './index.css'
 import App from './App.jsx'
 
-createRoot(document.getElementById('root')).render(
-  <StrictMode>
-    <App />
-    <Toaster
-      position="bottom-center"
-      toastOptions={{
-        style: {
-          background: 'var(--bg-overlay)',
-          color: 'var(--text-primary)',
-          border: '1px solid var(--border)',
-          fontSize: 'var(--text-sm)',
-          fontFamily: 'var(--font-sans)',
-        },
-      }}
-    />
-  </StrictMode>,
-)
+// Load deployment config before rendering — non-blocking (fallback kicks in on failure)
+loadConfig().then(() => {
+  createRoot(document.getElementById('root')).render(
+    <StrictMode>
+      <App />
+      <Toaster
+        position="bottom-center"
+        toastOptions={{
+          style: {
+            background: 'var(--bg-overlay)',
+            color: 'var(--text-primary)',
+            border: '1px solid var(--border)',
+            fontSize: 'var(--text-sm)',
+            fontFamily: 'var(--font-sans)',
+          },
+        }}
+      />
+    </StrictMode>,
+  )
+})