feat(obsidian): add collapsible folder tree for browsing notes

Replaced flat list with hierarchical folder tree structure for better
navigation when browsing vault notes.

**Features:**
- Collapsible folders with ▼/▶ toggle arrows
- Proper indentation showing folder hierarchy
- 📁 folder and 📄 file icons
- Click folder name to expand/collapse
- Click file to select it
- Handles root-level files and nested folders
- Hover highlights for files

**Functions added:**
- buildFolderTree(): Converts flat note list to tree structure
- renderFolderTree(): Recursively renders folders with nesting
- renderFiles(): Renders files at current folder level

Perfect for vaults organized like:
```
State1/
  Province1/
    City1.md
    City2.md
  Province2/
    City3.md
State2/
  Province3/
    City4.md
```

Much easier to navigate than a flat list of 100+ notes!

index.html

@@ -8282,7 +8282,7 @@
     <script defer src="modules/io/cloud.js?v=1.106.0"></script>
     <script defer src="modules/io/export.js?v=1.108.11"></script>
     <script defer src="modules/io/obsidian-bridge.js?v=1.108.13.3"></script>
-    <script defer src="modules/ui/obsidian-notes-editor.js?v=1.108.13.3"></script>
+    <script defer src="modules/ui/obsidian-notes-editor.js?v=1.108.13.4"></script>
     <script defer src="modules/ui/obsidian-config.js?v=1.108.13"></script>
 
     <script defer src="modules/renderers/draw-features.js?v=1.108.2"></script>