Add invitation frontend: invite modal, pending invitations, no-company view

Members Index:
- "Invite Member" button opens InviteMemberModal (email + role dropdown)
- Pending invitations section shows below members table with cancel buttons
- Members store gains inviteMember, fetchPendingInvitations, cancelInvitation

CompanySwitcher:
- Shows pending invitations greyed out below active companies
- Each with Accept/Decline mini-buttons
- Accepting refreshes bootstrap and switches to new company

NoCompanyView:
- Standalone page for users with zero accepted companies
- Shows pending invitations with Accept/Decline or "no companies" message
- Route: /admin/no-company

Invitation Pinia store:
- Manages user's own pending invitations (fetchPending, accept, decline)
- Bootstrap populates invitations from API response

Global store:
- Bootstrap action stores pending_invitations from response

lang/en.json

@@ -26,6 +26,9 @@
     "save": "Save",
     "create": "Create",
     "cancel": "Cancel",
+    "accept": "Accept",
+    "decline": "Decline",
+    "welcome": "Welcome",
     "update": "Update",
     "deselect": "Deselect",
     "download": "Download",