feat: add default map setting feature

Add ability to set a specific map as the default that opens on load:

- Add 'Open default map' option to onload behavior dropdown
- Implement saveAsDefaultMap() to store map as default in IndexedDB
- Implement clearDefaultMap() to remove default map setting
- Modify checkLoadParameters() to load default map when configured
- Add UI buttons in Save dialog for setting/clearing default map
- Update version to 1.108.12 and hash in index.html

Users can now:
1. Open any map they want as default
2. Go to Options > Onload behavior > Select "Open default map"
3. Save > Click "Set as default" button
4. The map will now open automatically every time

This sets the foundation for the planned time-based worldbuilding
and lore database features by ensuring users always start with
their primary world map.

versioning.js

@@ -13,7 +13,7 @@
  * Example: 1.102.2 -> Major version 1, Minor version 102, Patch version 2
  */
 
-const VERSION = "1.108.11";
+const VERSION = "1.108.12";
 if (parseMapVersion(VERSION) !== VERSION) alert("versioning.js: Invalid format or parsing function");
 
 {