Implement devlog entry edit <id>

[gustmrg]

Add support for editing an existing entry via devlog entry edit .

Context:

• README.md documents devlog entry edit
• The entry command currently only wires add and list
• Entries are stored in date-based JSON files under ~/.devlog/entries/

Expected behavior:

• Find an entry by its ID
• Open an interactive prompt to edit the entry
• Show current values as defaults
• Allow pressing Enter to keep the current value
• Save the updated entry back to the correct daily log file

Implementation notes:

• Entry lookup will likely require scanning stored daily log files for the matching id
• Editable fields should at least include:
  • project
  • description
  • tags
  • date if date changes are intended to be supported
• If date changes are supported, move the entry to the appropriate daily log file
• Return a clear error when the ID is not found

Acceptance criteria:

• devlog entry edit exists and appears in help output
• Existing entry values are shown during the edit flow
• Pressing Enter preserves existing values
• Updated data is persisted correctly
• Missing IDs produce a clear, user-friendly error