feat(ui+backend): base of data persistence

internal/graph/mutation.graphql

@@ -2,6 +2,26 @@ input UserChanges {
   name: String
 }
 
+input CreateProjectChanges {
+  title: String!
+}
+
+input ProjectTaskChanges {
+  label: String
+  categoryId: ID
+  estimations: ProjectTaskEstimationsChanges
+}
+
+input ProjectTaskEstimationsChanges {
+  optimistic: Float
+  likely: Float
+  pessimistic: Float
+}
+
 type Mutation {
   updateUser(id: ID!, changes: UserChanges!): User!
+  createProject(changes: CreateProjectChanges!): Project!
+  updateProjectTitle(projectId: ID!, title: String!): Project!
+  addProjectTask(projectId: ID!, changes: ProjectTaskChanges): Task!
+  removeProjectTask(projectId: ID!, taskId: ID!): Boolean!
 }