Add milestone creation and editing

crates/app/src/lib.rs

@@ -458,6 +458,57 @@ impl GotchaCore {
         ))
     }
 
+    pub async fn milestone_editor(
+        &self,
+        owner: String,
+        repository: String,
+        id: Option<i64>,
+    ) -> Result<MilestoneEditorPage, GotchaError> {
+        let (owner, repository) = validate_repository(&owner, &repository)?;
+        if id.is_some_and(|id| id <= 0) {
+            return Err("Invalid milestone selection.".into());
+        }
+        let milestone = match id {
+            Some(id) => Some(load_milestone_editor(&self.server()?, owner, repository, id).await?),
+            None => None,
+        };
+        Ok(milestone_editor_page(milestone))
+    }
+
+    pub async fn save_milestone(
+        &self,
+        owner: String,
+        repository: String,
+        id: Option<i64>,
+        title: String,
+        description: String,
+        due_date: Option<i64>,
+    ) -> Result<i64, GotchaError> {
+        let (owner, repository) = validate_repository(&owner, &repository)?;
+        let title = title.trim();
+        if title.is_empty() {
+            return Err("Enter a milestone title.".into());
+        }
+        if id.is_some_and(|id| id <= 0) {
+            return Err("Invalid milestone selection.".into());
+        }
+        let milestone = save_milestone(
+            &self.server()?,
+            owner,
+            repository,
+            id,
+            MilestoneDraft {
+                title: title.into(),
+                description,
+                due_date,
+            },
+        )
+        .await?;
+        milestone
+            .id
+            .ok_or_else(|| "The saved milestone has no ID.".into())
+    }
+
     pub async fn pull_filters(&self) -> Result<PullFilterOptions, GotchaError> {
         let server = self.server()?;
         let filter = self