fix: reduce editor minimum width and padding at narrow sizes

Halve the editor min-width from 800px to 400px so the window can be
resized narrower. Add a container query that reduces horizontal padding
from 40px to 16px when the editor panel is under 600px wide, keeping
content readable without wasting space on padding.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/Editor.css

@@ -359,3 +359,13 @@
 .editor__blocknote-container [data-node-type="blockContainer"]:first-child:has([data-content-type="heading"][data-level="1"]) {
   display: none;
 }
+
+/* Reduce padding at narrow editor widths so content isn't cramped */
+@container editor (max-width: 600px) {
+  .editor__blocknote-container .bn-editor {
+    padding: 12px 16px;
+  }
+  .title-section {
+    padding: 0 16px;
+  }
+}