VERSION 4
=========
1. Added Clients module:
   - Register client/company
   - Contact person, phone, email, address, notes, status
   - Shows number of posts hired and total guards required
   - Shows posts linked to each client
2. Added Guard Assignment / Deployment module:
   - Assign active guards to posts
   - Day/Night shift
   - Effective start and end dates
   - Replacement/Reliever field
   - Assignment history
   - End an active deployment
   - Pagination (10 per page)
3. Updated navigation and dashboard with Active Clients and Active Deployments.
4. Updated roster generator to use active Guard Deployments for post and shift instead
   of randomly assigning guards to posts. Guards without a valid deployment are marked
   as Duty with a note so management can correct the deployment.
5. Added database/update_v4.sql for EXISTING databases.
6. Updated fresh database/security_management.sql with the new fields.
7. Existing posts are preserved when applying update_v4.sql.
