fix: convert __NONE__ project placeholder to empty string

[ShivaGupta-14]

Description

• Fixes bug where selecting "No project" stored "NONE" instead of empty string. Added unit test for this edge case.

• Fixes: Selecting No project as Project on Add Task adds a __None__ value by default #377

Additional Bug Found

While testing this fix, I discovered a related crash bug:

Steps to reproduce (before fix):

1. Open "Add Task" dialog
2. Click "No project"
3. Click "Create new project"
4. App crashes with black screen and removeChild DOM error

Video:

Before:

Screen.Recording.2026-01-06.at.7.05.30.PM.mov

After:

Screen.Recording.2026-01-06.at.7.10.31.PM.mov

• This fix resolves both issues

Checklist

• Ran npx prettier --write . (for formatting)
• Ran gofmt -w . (for Go backend)
• Ran npm test (for JS/TS testing)
• Added unit tests, if applicable
• Verified all tests pass
• Updated documentation, if needed

Additional Notes

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[ShivaGupta-14]

converts NONE to empty string when "No project" is selected

[ShivaGupta-14]

added unit test

[ShivaGupta-14]

self review done! ready for review