Fix embed command ignoring defaultFolder destination setting

[bberak]

Summary

🚨NOTE: This PR (including code) was created with Claude Code.

• When creating a new drawing via the / embed command, attachTo is always set to the current file. The condition (attachTo || destinationMethod === 'attachments-folder') in getTldrawFileDestination therefore always short-circuits to true, causing the file to be saved to Obsidian's core attachmentFolderPath regardless of the plugin's destinationMethod setting.
• Users who set destinationMethod to "default-folder" (e.g. "Drawings") have their preference silently ignored for embed commands — files end up in the vault's attachment folder instead.
• The fix replaces the short-circuiting if with a direct switch on destinationMethod, so attachTo no longer overrides the configured destination.

Steps to reproduce

1. Set destinationMethod to "default-folder" and defaultFolder to any folder (e.g. "Drawings")
2. Set confirmDestination to false
3. Set Obsidian's core attachmentFolderPath to a different folder (e.g. "Attachments")
4. Open a note and use the / slash command to embed a new tldraw drawing
5. Expected: file is created in "Drawings"
6. Actual: file is created in "Attachments"

Note: when confirmDestination is true, the confirmation modal works correctly because it builds the destination list independently without the attachTo short-circuit.

Test plan

• Verify embed command respects defaultFolder when destinationMethod is "default-folder" and confirmDestination is false
• Verify embed command still uses Obsidian's attachment folder when destinationMethod is "attachments-folder"
• Verify colocate mode still works for embed commands
• Verify non-embed "create new drawing" commands still work correctly
• Verify confirmDestination: true still works as before