Use .relayignore exclusions and refresh sharing state

[MDerman]

Why

I want Relay to support local-only folders inside a shared folder. Some folders should stay on my device while the rest of the shared folder continues syncing normally.

While testing shared folders, I also found places where Relay state in Obsidian could look stale: users, roles, and newly available folders sometimes did not refresh until Obsidian was restarted. This PR also tightens those refresh paths so changes show up in the UI without a restart.

What changed

• Added .relayignore as a local marker file for folders Relay should not sync.
• Added folder context-menu actions to stop syncing or resume syncing a folder.
• Added a small cloud-off indicator in Obsidian's file explorer for ignored folders.
• Added a cleanup prompt for remote Relay metadata that already exists under an ignored folder.
• Refreshed shared-folder state after marker, user, role, and folder changes so Obsidian does not need a restart.

Implementation

SharedFolder now tracks ignored marker roots and skips matching local and remote paths. The .relayignore file itself is treated as local control metadata, so it is never uploaded as a Relay file.

Marker scan/create/remove uses Obsidian's vault adapter instead of only the metadata tree. This matters because hidden dotfiles can exist on disk without appearing reliably in Obsidian's file cache.

Rename and move handling now checks whether a path is moving into, out of, or within an ignored subtree. Relay can then decide whether to skip the change, upload it, move existing metadata, or remove sync metadata for ignored content.

The file explorer indicator reuses Relay's existing folder navigation walker. Directly ignored folders get the stronger cloud-off marker; folders ignored by a parent marker get a muted marker.

The refresh changes update Relay's local folder/user state after relevant changes, so the settings UI and folder list do not depend on an Obsidian restart to catch up.

Tests

Added focused tests for the marker-based ignore policy:

• .relayignore marks its parent folder and descendants ignored.
• Sibling folders remain syncable.
• The .relayignore marker itself is never syncable.
• Rename/move classification covers syncable-to-syncable, syncable-to-ignored, ignored-to-syncable, and ignored-to-ignored transitions.
• Remote cleanup collects ignored entries under marker roots, deepest paths first.

Validation run:

• npm test -- src/ignoredFolderPolicy.test.ts src/privateFolderIgnore.test.ts
• npm run build

I kept these tests outside the encrypted/binary SharedFolder test fixture in this checkout, so the new behavior is covered in small policy tests that can run normally.