Docs: how SessionListRequest.Directory matches #304

What

The docs don't say how SessionListRequest.Directory matches. Is it an exact directory or also its descendants, and is the path normalized (case, separators, trailing slash)? The web dashboard's builder had to guess when it scoped its session list.

Proposed

Document the matching that upstream applies to the session list's directory filter, on SessionListRequest.Directory and in the guide.

Source: internal DevEx evaluation, web-dashboard round, 2026-10-15 (finding W-2).