Dashboard 'my session' counts include other users' sessions for admins (same root cause as FR-3092)

## Context

Same root pattern as FR-3092 (fixed for `/session` in PR #7838): `react/src/pages/DashboardPage.tsx:83` passes `scopeId: \`project:${currentProject.id}\`` into `SessionCountDashboardItemFragment` / `RecentlyCreatedSessionFragment`, whose aliases are literally `myInteractive`, `myBatch`, … (`react/src/components/SessionCountDashboardItem.tsx:44-70`). For admin/monitor roles the backend returns all project sessions, so the dashboard's 'my session' counts and 'recently created sessions' include other users' sessions.

## Fix

Apply the same `user_id == ""` filter merge as PR #7838 (fragments take `scopeId` via `@argumentDefinitions`; add a user-filter argument or merge into the literal filters the same way).

JIRA Issue: FR-3107

Start with react/src/pages/DashboardPage.tsx:83 and the fragment definitions in react/src/components/SessionCountDashboardItem.tsx:44-70. Compare the scopeId and user-filter merge used for /session in PR #7838, then apply the corresponding filter to these dashboard fragments. Done means admin and monitor dashboards count only the current user's sessions and recent sessions.

Written by the indexing model from the issue text.