feat: add --content flag to daily command

[Yakitrak]

Summary

• Adds --content / -c flag to the daily command, closing Daily command should also allow adding content #119
• New notes are created with template + content combined
• Existing notes get content appended automatically (no --append flag needed)
• Reuses WriteNoteFile and NormalizeContent from create command

Test plan

• Unit tests for content-only creation, template+content, append to existing, no-op without content
• Full test suite passes
• Manual testing with and without editor flag

Closes #119