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.

.vscode/tasks.json

@@ -0,0 +1,13 @@
+{
+	"version": "2.0.0",
+	"tasks": [
+		{
+			"label": "Dev Server",
+			"type": "shell",
+			"command": "pnpm dev",
+			"group": "build",
+			"isBackground": true,
+			"problemMatcher": []
+		}
+	]
+}