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.

packages/lib/server-only/team/analytics-period.ts

@@ -0,0 +1,84 @@
+import { DateTime } from 'luxon';
+import { match } from 'ts-pattern';
+import { z } from 'zod';
+
+/**
+ * Calendar period presets for the team analytics dashboard. Each resolves to a
+ * half-open `[start, end)` instant range in the viewer's timezone.
+ *
+ * Pure (zod + luxon, no Prisma) so it can be unit-tested without a database and
+ * shared with the request schema without pulling server-only code anywhere it
+ * should not go.
+ */
+export const ZAnalyticsPeriodSchema = z.enum([
+  'week',
+  'month',
+  'quarter',
+  'year',
+  'lastMonth',
+  'last7Days',
+  'last30Days',
+]);
+
+export type AnalyticsPeriod = z.infer<typeof ZAnalyticsPeriodSchema>;
+
+export const DEFAULT_ANALYTICS_PERIOD: AnalyticsPeriod = 'month';
+
+export type AnalyticsPeriodRange = {
+  start: Date;
+  end: Date;
+};
+
+/**
+ * Resolve a calendar preset into a half-open `[start, end)` instant range,
+ * anchored to the viewer's timezone.
+ *
+ * Falls back to UTC when the zone is missing or invalid so boundaries never
+ * silently drift to the server's local zone.
+ */
+export const resolveAnalyticsPeriod = ({
+  period,
+  timezone,
+}: {
+  period: AnalyticsPeriod;
+  timezone?: string;
+}): AnalyticsPeriodRange => {
+  const zoned = DateTime.now().setZone(timezone ?? 'utc');
+  const now = zoned.isValid ? zoned : DateTime.now().setZone('utc');
+
+  const { start, end } = match(period)
+    .with('week', () => ({
+      start: now.startOf('week'),
+      end: now.startOf('week').plus({ weeks: 1 }),
+    }))
+    .with('month', () => ({
+      start: now.startOf('month'),
+      end: now.startOf('month').plus({ months: 1 }),
+    }))
+    .with('quarter', () => ({
+      start: now.startOf('quarter'),
+      end: now.startOf('quarter').plus({ quarters: 1 }),
+    }))
+    .with('year', () => ({
+      start: now.startOf('year'),
+      end: now.startOf('year').plus({ years: 1 }),
+    }))
+    .with('lastMonth', () => ({
+      start: now.startOf('month').minus({ months: 1 }),
+      end: now.startOf('month'),
+    }))
+    .with('last7Days', () => ({
+      start: now.startOf('day').minus({ days: 6 }),
+      end: now.startOf('day').plus({ days: 1 }),
+    }))
+    .with('last30Days', () => ({
+      start: now.startOf('day').minus({ days: 29 }),
+      end: now.startOf('day').plus({ days: 1 }),
+    }))
+    .exhaustive();
+
+  return {
+    start: start.toJSDate(),
+    end: end.toJSDate(),
+  };
+};