feat: Cmd+N for sibling notes, edit focus improvements

[careck]

Summary

• Cmd+N remapped from New Workspace to Add Sibling Note (more frequently used action)
• Cmd+Shift+N stays as Add Child Note (label updated from generic "Add Note")
• New Workspace remains in File menu, just without a keyboard shortcut
• AddNoteDialog auto-focuses the type dropdown and pre-selects the sibling's schema type
• Edit mode focuses the first schema field when the title field is hidden by the schema
• Tag input no longer traps Tab/Enter when empty, allowing keyboard navigation and quick save

Test plan

• Cmd+N with a note selected opens Add Sibling dialog with correct type pre-selected
• Cmd+Shift+N opens Add Child dialog as before
• Type dropdown is focused on dialog open — arrow keys change selection
• With a schema that hides the title, entering edit mode focuses the first field
• Tab moves through fields past an empty tag input; Tab with text in tag input still adds the tag
• Enter on an empty tag input saves the note; Enter with text adds the tag
• New Workspace still accessible from File menu (no shortcut)
• All 7 locales display correct menu labels