New 'separate copy' concept for a session's project location and sync status

What

• Tool-context location descriptions gained a "separate" case describing a location as the session's own dedicated checkout — "the primary copy for this session's work" — alongside the existing default/machine/unknown cases.
• The device/session sync telemetry payload gained an optional folder_relation field that accepts the value separate_copy, alongside the existing project_sync enum.
• The status text describing a session's synced project directory gained a new case for when the project is the user's own separate copy with sync turned off, showing distinct wording instead of falling back to a generic "not synced" message.

Why

This gives Claude Code a consistent way to describe and record when a session is working from its own separate checkout rather than a directly synced copy, making status messages and sync telemetry clearer.