Each scope reports only the dashboard sessions recorded in it

[SaulMoro]

Parent

#752 (items 1 and 4)

What to build

Each scope reports only the dashboard sessions recorded in it. Today every scope reads one machine-wide event stream and tells its own sessions apart by a cwd string prefix. That breaks in three ways: Copilot sends no cwd, a symlinked or /tmp vs /private/tmp path never matches, and the user scope excludes nothing, so it reports every project's sessions.

 hook event
-  → events.jsonl { cwd?, … }
+  → events.jsonl { scope: <dataHome key of the resolved scope>, cwd?, … }

 report for scope S
-  keep events whose cwd starts with S's root      (user scope: keep everything)
+  keep events whose scope is S
+  events written before this change (no scope):
+    project → its cwd, realpath'd, is under the project root
+    user    → never

The event stream stays machine-wide: the teamai dashboard UI, stats --by-repo, session save and the contribute check read across scopes, and the data-directory design documents it as a machine-level singleton. The hook dispatcher already knows the scope when it writes, since #769 hands every handler the config it resolved.

Also: document how to remove a skill entry that was pushed before #748 from stats/<user>.yaml on teamai-reports by hand. Those events carry no cwd, so nothing can attribute them after the fact. Docs only, no command.

Acceptance criteria

• A user-scope pull does not report a session recorded in project P; P's own pull still does.
• A Copilot session in P is reported by P.
• A session started under a symlinked path of P is reported by P.
• Old events without a scope go to their project, never to the user scope.
• The dead excludeProjectRoots path is gone.
• The usage guide (both languages) explains the manual stats/<user>.yaml cleanup; data-directory design and CHANGELOG updated.
• Verified with the real CLI (Claude; git, gitlab, github providers).

Blocked by

None (can start immediately).

[SaulMoro]

Rule change, decided while fixing the CI review on #791: an event written before this change (no data-home key) is not dropped by the user scope any more. The user scope keeps such an event when its cwd still exists and resolves to the user scope now (the dispatcher's own rule, resolveConfigForDir). Events without a cwd, or whose cwd was deleted, go to no scope, so no project's session reaches the user-scope team.