snapshots: clicking copy-event source should navigate to that install

Follow-up to #781 / #801.

## Context

The Snapshots tab timeline renders "copy events" (when this install was created as a copy of another install) as a row showing the source's name and the copy timestamp. The source name is currently plain text:

https://github.com/Comfy-Org/ComfyUI-Desktop-2.0-Beta/blob/main/src/renderer/src/views/comfyUISettings/SnapshotsView.vue#L976-L986

## Proposal

Make the `{source}` portion of the label a hyperlink that navigates to the source install's panel (same target the picker uses when you select that install). When the source install no longer exists, fall back to plain text (or a disabled chip) so users see the historical name but don't get a dead click.

## Things to consider / scope

- **Existence check** - `CopyEvent` only carries `installationId` + `installationName` + `copiedAt`. The renderer needs to know whether an install with that id still exists before deciding link vs. plain text. Either fetch the install list it already has access to, or extend the IPC payload with a boolean.
- **Navigation target** - pick the matching existing primitive (panel switch IPC, picker selection, etc.) so we don't invent a new route.
- **Missing source UX** - disabled link with a tooltip ("Install no longer exists") vs. plain text vs. struck-through name - needs a quick design call.
- **A11y** - the label currently sits inside a `` group with an icon + time; the link should be the inner name only, with a clear accessible name.

Splitting this out of #781 so that PR stays a minimal locale fix.