Add Activity Timeline feature and database migrations

- Add Activity Timeline tab to ticket view showing chronological history
- Create getTicketTimeline() method in AuditLogModel
- Update TicketController to load timeline data
- Add timeline UI with helper functions for formatting events
- Add comprehensive timeline CSS with dark mode support
- Create migrations 007-010 for upcoming features:
  - 007: Ticket assignment functionality
  - 008: Status workflow transitions
  - 009: Ticket templates
  - 010: Bulk operations tracking

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

migrations/007_add_ticket_assignment.sql

@@ -0,0 +1,13 @@
+-- Migration 007: Add ticket assignment functionality
+-- Adds assigned_to column to tickets table
+
+-- Add assigned_to column to tickets table
+ALTER TABLE tickets
+    ADD COLUMN assigned_to INT NULL,
+    ADD CONSTRAINT fk_tickets_assigned_to
+        FOREIGN KEY (assigned_to)
+        REFERENCES users(user_id)
+        ON DELETE SET NULL;
+
+-- Add index for performance
+CREATE INDEX idx_assigned_to ON tickets(assigned_to);