feat: add staging and overlap detection operations

Introduces functions to stage files, unstage all changes, and detect
unstaged overlaps with staged files. Enables better git workflow control
and prevents accidental commits with conflicting changes.

Author: Sephyi

src/services/git.rs

@@ -255,6 +255,44 @@ impl GitService {
         )
     }
 
+    // ─── Staging Operations ───
+
+    /// Check if any staged file also has unstaged modifications.
+    /// Returns the list of overlapping file paths.
+    pub async fn has_unstaged_overlap(&self) -> Result<Vec<PathBuf>> {
+        let (staged_output, unstaged_output) = tokio::try_join!(
+            self.run_git(&["diff", "--cached", "--name-only"]),
+            self.run_git(&["diff", "--name-only"]),
+        )?;
+
+        let staged: std::collections::HashSet<&str> =
+            staged_output.lines().filter(|l| !l.is_empty()).collect();
+        let unstaged: std::collections::HashSet<&str> =
+            unstaged_output.lines().filter(|l| !l.is_empty()).collect();
+
+        Ok(staged.intersection(&unstaged).map(PathBuf::from).collect())
+    }
+
+    /// Unstage all currently staged files (soft reset).
+    pub async fn unstage_all(&self) -> Result<()> {
+        self.run_git(&["reset", "HEAD"]).await?;
+        Ok(())
+    }
+
+    /// Stage specific files by path.
+    pub async fn stage_files(&self, paths: &[PathBuf]) -> Result<()> {
+        if paths.is_empty() {
+            return Ok(());
+        }
+
+        let path_strs: Vec<String> = paths.iter().map(|p| p.display().to_string()).collect();
+        let mut args: Vec<&str> = vec!["add", "--"];
+        args.extend(path_strs.iter().map(|s| s.as_str()));
+
+        self.run_git(&args).await?;
+        Ok(())
+    }
+
     // ─── Commit ───
 
     pub async fn commit(&self, message: &str) -> Result<()> {