[Feature] CLI open vault and open folder

[radiorambo]

CLI can only open files from file paths like zen open path/to/file.md, but having an option to

• open vaults like zen open path/to/vault
• open a specific folder like zen option path/to/folder.

Difference between opening vault and folder is that opening folder is useful when I don't want to create a vault but want to focus on particular folder like when reading a docs folder in code repo, or when I have planning my morning routine, I want to open my "plans" folder without the noise of other folders in the vault via script.

[adibhanna]

Done — zn open now accepts a folder, not just markdown files.

• zn open ~/code/project/docs (or any folder) opens a focused, non-persisted session scoped to that folder: a window that shows only that folder's notes, with no vault registered. That's the way to read a repo's docs/ folder, or zoom into one folder of a big vault (e.g. plans/) without the noise of everything else.
• zn open ~/notes opens a vault the same way (and just focuses the window if it's already open).
• Files still open as notes and must be markdown; folders skip that check.

Under the hood the app already treated a dropped folder as a scoped session — this wires it up from the CLI, and reuses an existing window if one is already open on that folder.

Verified end-to-end: zn open ~/project/docs opened a window titled docs showing only that folder's notes (a src/*.js file in the same project was correctly ignored).

Ships in v2.17.0. Thanks for the clear write-up on the vault-vs-folder distinction — that framing made it easy to scope.