feat: add multi-BU tenancy with per-user team scoping (Option B)

- Add bu_teams column to users table (migration + fresh schema)
- Create shared KNOWN_TEAMS constant and validateTeams helper
- Expose user teams in auth middleware, login, and /me responses
- Add bu_teams CRUD to user management routes with audit logging
- Make Ivanti FINDINGS_FILTERS configurable via IVANTI_BU_FILTER env var
- Add query-time team filtering to GET /findings and /findings/counts
- Update AuthContext with teams helpers and admin scope toggle
- Create AdminScopeToggle component (My Teams / All BUs)
- Scope ReportingPage findings fetch by user teams
- Scope CompliancePage team selector by user teams
- Scope ExportsPage findings exports by user teams
- Add BU teams multi-select to UserManagement create/edit forms
- Display team badges in user list table

backend/middleware/auth.js

@@ -12,7 +12,7 @@ function requireAuth(db) {
         try {
             const session = await new Promise((resolve, reject) => {
                 db.get(
-                    `SELECT s.*, u.id as user_id, u.username, u.email, u.role, u.user_group, u.is_active
+                    `SELECT s.*, u.id as user_id, u.username, u.email, u.role, u.user_group, u.bu_teams, u.is_active
                      FROM sessions s
                      JOIN users u ON s.user_id = u.id
                      WHERE s.session_id = ? AND s.expires_at > datetime('now')`,
@@ -38,7 +38,8 @@ function requireAuth(db) {
                 username: session.username,
                 email: session.email,
                 role: session.role,
-                group: session.user_group
+                group: session.user_group,
+                teams: session.bu_teams ? session.bu_teams.split(',').filter(Boolean) : []
             };
 
             next();