feat(backend): add problem/need submission module with workflow and events

Add submission CRUD with pagination and role scoping, challenge/location binding, automatic keyword extraction, a validated status workflow, and domain events for matchmaking and notifications. Create a problem record together with each submission.

backend/Infrastructure/Persistence/SurrealRows.cs

@@ -34,3 +34,33 @@ internal sealed class ConsentRow
 
     [CborProperty("revoked_at")] public DateTimeOffset? RevokedAt { get; set; }
 }
+
+internal sealed class SubmissionRow
+{
+    [CborProperty("id")] public string Id { get; set; } = string.Empty;
+
+    [CborProperty("problem")] public string Problem { get; set; } = string.Empty;
+
+    [CborProperty("status")] public string Status { get; set; } = string.Empty;
+
+    [CborProperty("keywords")] public List<string> Keywords { get; set; } = [];
+
+    [CborProperty("created_at")] public DateTimeOffset CreatedAt { get; set; }
+
+    [CborProperty("updated_at")] public DateTimeOffset? UpdatedAt { get; set; }
+
+    [CborProperty("title")] public string Title { get; set; } = string.Empty;
+
+    [CborProperty("description")] public string Description { get; set; } = string.Empty;
+
+    [CborProperty("challenge")] public string Challenge { get; set; } = string.Empty;
+
+    [CborProperty("location")] public string Location { get; set; } = string.Empty;
+
+    [CborProperty("author")] public string Author { get; set; } = string.Empty;
+}
+
+internal sealed class CountRow
+{
+    [CborProperty("count")] public int Count { get; set; }
+}