[applet] Improve presentation and consistency for vault items
This MR includes the following UI improvements:
- Use more familiar and appropriate lock/unlock style icons for the default action instead of mount/unmount
- Change action verbs to "lock"/"unlock" to match the icon and reinforce the security angle
- Conditionally change text of "open with file manager" action to reflect the vault's locked/unlocked status
- Use consistent Title Case for action items
After, vault is locked:
After, vault is unlocked:
cc @teams/vdg