Monzer V3 fixes - 2026-06-10

1) Lead view: Added By added inside lead view using created_by_user_id / created_by_name.
2) Lead view: removed Edit Note button; note is display only in view.
3) Send from Lead: rebuilt as tab UI like customer contact tabs (WhatsApp / Email), with professional preview.
   - WhatsApp tab shows WhatsApp-style preview and supports item image or uploaded image.
   - Email tab shows email subject + message and supports item image/upload image.
4) Send from Lead now posts to handlers/communications.php with target_type=lead, customer_id, lead_id, type, message, subject, include_item_image, and media.
5) Campaign form: cannot save if Saved Audience is not selected.
6) Campaign form: cannot save if Dynamic Filter has no selected filters/customers.
7) Campaign handler: server-side block prevents saving campaigns with no audience/no matching customers.
8) Removed Preview Customers button from audience add/edit.
9) Removed Preview Customers button from campaign add/edit if present.
10) Reminder calendar: added Previous Month / Current Month / Next Month navigation, month title, weekday header, selected day support.
11) Clicking calendar day filters the reminder list to that exact date.
12) Full PHP syntax check passed for project files.
