feat(backend): add communication, tester, admin and middleman modules

Implement step 17 modules: threads/messages, notifications with automation (submission.created, idea.created, grant_call.opened), innovation test feedback, admin panel (submissions, verify, metrics, grant call status), Middleman adaptation and partnerships. Split multi-type files into one type per file and replace object-valued dictionaries with string-valued maps in data contracts (migrations 0006/0007).

backend/Application/Security/Policies.cs

@@ -0,0 +1,20 @@
+namespace TarninaHub.Application.Security;
+
+
+public static class Policies
+{
+    /// <summary>operator, manager, admin — ROPS/expert staff.</summary>
+    public const string Staff = "Staff";
+
+    /// <summary>operator, admin.</summary>
+    public const string OperatorOrAdmin = "OperatorOrAdmin";
+
+    /// <summary>manager, operator, admin.</summary>
+    public const string ManagerOrAbove = "ManagerOrAbove";
+
+    /// <summary>admin only.</summary>
+    public const string AdminOnly = "AdminOnly";
+
+    /// <summary>jst and above (jst, operator, manager, admin).</summary>
+    public const string JstOrAbove = "JstOrAbove";
+}