Reveal in Finder and Edit config from a project's context menu

[aosmcleod]

Right-clicking a project offers Remove Project and pinning. Two more belong there:

• Reveal in Finder — opens the repository directory
• Edit config — opens the project's .conf in the default editor

The second is a deliberate escape hatch. Everything in the config is editable in the app now, but a text editor is still the fastest way to read the whole thing, and the file being plain and hand-editable is a feature rather than an embarrassment.

Careful about

• Reveal should point at the repository, not at a Runbranch-managed worktree, since the repository is what the user thinks of as the project.
• If the config is edited externally while the app is open, the app's in-memory copy is stale. Re-reading on window focus would cover it; at minimum this should not silently overwrite an external edit.

Good first issue.