Adds email approval & Postmark integration for negotiations

Enables users to approve and send negotiation emails directly via Postmark after configuring a server token in settings. Introduces new debt statuses ("approved", "sent"), UI for token management, and approval/rejection flows. Refactors notifications to use a modern toast library, adjusts dashboard status filters, and updates DB schema for new flows.

Empowers compliant, user-controlled negotiation and automated email delivery.

supabase/migrations/20250607009000_add_postmark_server_token.sql

@@ -0,0 +1,14 @@
+/*
+  # Add Postmark Server Token
+
+  1. Changes
+    - Add postmark_server_token column to user_profiles table
+    - This will be used for sending approved emails
+*/
+
+-- Add postmark_server_token to user_profiles
+ALTER TABLE user_profiles 
+ADD COLUMN IF NOT EXISTS postmark_server_token text;
+
+-- Add comment for documentation
+COMMENT ON COLUMN user_profiles.postmark_server_token IS 'Postmark server token for sending approved negotiation emails';