feat: add move file/directory option to FileTree context menu

[rjroy]

Summary

• Adds a Move option to the FileTree context menu for files and directories
• Opens a dialog with a mini file tree for selecting the destination directory
• Shows live path preview of the destination location
• Automatically updates all wikilinks and markdown links after moving
• Prevents moving directories into themselves or their subdirectories

Closes #330

Test plan

• Open the Recall tab and navigate the file tree
• Right-click a file and select "Move" from the context menu
• Verify the MoveDialog opens with a mini file tree
• Select a different destination directory and verify the path preview updates
• Click Move and verify the file is moved to the new location
• Verify any wikilinks/markdown links to the file are updated
• Test moving a directory and verify contents are preserved
• Verify you cannot move a directory into itself or its subdirectories

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 93.36870% with 25 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
frontend/src/components/MoveDialog.tsx	91.76%	14 Missing ⚠️
frontend/src/components/FileTree.tsx	80.76%	10 Missing ⚠️
frontend/src/components/BrowseMode.tsx	85.71%	1 Missing ⚠️

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