fix: block editor visibility — flex layout + 400ms init delay

- page-editor-wrapper: min-height:0 + display:flex column to prevent collapse
- blocks-container: flex:1 to fill remaining space
- init setTimeout: 200→400ms for reliable Alpine render
- Removed min-height:100% that caused overflow clipping

static/css/app.css

@@ -1510,7 +1510,9 @@ input, select, textarea { font-family: inherit; color: inherit; }
   flex: 1;
   overflow-y: auto;
   padding: 0;
-  min-height: 100%;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
 }
 
 /* Page title area */
@@ -1558,6 +1560,7 @@ input, select, textarea { font-family: inherit; color: inherit; }
   max-width: 900px;
   margin: 0 auto;
   min-height: 300px;
+  flex: 1;
 }
 
 .blocks-empty {