feat(team): add team analytics dashboard

Add a team document-usage dashboard at /t/:teamUrl/analytics for team admins and managers,
behind the NEXT_PUBLIC_FEATURE_TEAM_ANALYTICS_ENABLED rollout flag (enabled by default, set to
"false" to gate it off).

Backend:
- getTeamAnalytics Kysely query over team-produced documents across all folders, with exact
  COUNT(*) (no STATS_COUNT_CAP). Each metric uses its own date axis: Sent/Draft/Pending by
  createdAt, Completed by Envelope.completedAt, Declined by the DOCUMENT_RECIPIENT_REJECTED
  audit-log timestamp.
- resolveAnalyticsPeriod turns calendar presets into half-open [start, end) ranges in the
  viewer's timezone, falling back to UTC.
- team.getAnalytics tRPC route gated to ADMIN/MANAGER.

Frontend:
- Standalone /t/:teamUrl/analytics route whose loader gates the flag and role, silently
  redirecting members to documents.
- Headline metrics and compact stat tiles, a member multiselect filter, a calendar-preset
  period selector, and an empty state.
- Role- and flag-gated nav entries in the desktop and mobile navigation.

Tests:
- Unit tests for the period resolver (timezone and preset boundaries).
- Integration/E2E tests for the query semantics (date axes, audit-log decline, all-folders
  aggregation, sender attribution), access control, filters and the empty state.

.env.example

@@ -160,6 +160,8 @@ NEXT_PRIVATE_REDIS_PREFIX="documenso"
 NEXT_PUBLIC_POSTHOG_KEY=""
 # OPTIONAL: Leave blank to disable billing.
 NEXT_PUBLIC_FEATURE_BILLING_ENABLED=
+# OPTIONAL: Team analytics dashboard kill-switch. Enabled by default; set to "false" to hide it during rollout.
+NEXT_PUBLIC_FEATURE_TEAM_ANALYTICS_ENABLED=
 # OPTIONAL: Set to "true" to disable all signup methods (email, Google, Microsoft, OIDC, including the organisation OIDC portal).
 NEXT_PUBLIC_DISABLE_SIGNUP=
 # OPTIONAL: Set to "true" to disable email/password signup only.