Admin: Add approved organizer to organization by email

[Logvin]

Summary

Admins should be able to associate a user with an organization directly from the organization detail screen, without having to navigate to Manage Users. This is the primary workflow for onboarding an organizer from a specific org.

Proposed UX

On the Organization detail screen (admin view), add an "Add Approved Organizer" section at the bottom of the panel:

• A single email input field
• An "Add" button
• On submit: look up the user by email in the users table
  • If found: create a user_orgs record linking the user to this org (if one doesn't already exist), and set their role to organizer if it is currently guest
  • If not found: create a new user row with that email, role organizer, and org_id set to this org, then create the user_orgs record
• Display the current approved organizers for this org in a list, with a Remove button next to each one

Acceptance Criteria

• "Add Approved Organizer" section visible on org detail panel (admin only)
• Email input + Add button; inline error if email is blank or invalid
• Existing user found by email → linked to org via user_orgs, role upgraded to organizer if guest
• No existing user → new user row created with that email and organizer role, linked to org
• Duplicate add (user already in org) → no-op or friendly message, no error
• Organizer list shows all users currently linked to this org
• Remove button unlinks user from org (deletes user_orgs row); does not delete the user
• A user can belong to multiple orgs (the existing user_orgs table already supports this)

Notes

• The user_orgs table already exists and supports many-to-many user↔org relationships
• The users.org_id FK is the user's primary org — linking via user_orgs is the correct path for multi-org membership
• No changes to the DB schema should be required