fix: use merge commit for PR number detection

.changelog/shy-bats-wave.md

@@ -0,0 +1,5 @@
+---
+changelogs: patch
+---
+
+Fixed PR number detection to use merge commit instead of file creation commit.

src/changelog_entry.rs

@@ -121,6 +121,44 @@ pub struct CommitInfo {
 pub fn get_commit_info(_changelog_dir: &Path, id: &str) -> Option<CommitInfo> {
     let file_path = format!(".changelog/{}.md", id);
 
+    // First, try to find the merge commit that brought this file into the current branch
+    // This gives us the PR number from the merge commit message (e.g., "Merge pull request #37")
+    let merge_output = std::process::Command::new("git")
+        .args([
+            "log",
+            "--merges",
+            "--ancestry-path",
+            "--format=%H %s",
+            "-1",
+            "--",
+            &file_path,
+        ])
+        .output()
+        .ok()?;
+
+    let merge_stdout = String::from_utf8_lossy(&merge_output.stdout);
+    let merge_line = merge_stdout.trim();
+
+    // If we found a merge commit, use it
+    if !merge_line.is_empty() {
+        let parts: Vec<&str> = merge_line.splitn(2, ' ').collect();
+        if parts.len() >= 2 {
+            let commit_sha = parts[0].to_string();
+            let commit_message = parts[1];
+            let pr_number = extract_pr_number(commit_message);
+
+            if pr_number.is_some() {
+                let authors = get_commit_authors(&file_path);
+                return Some(CommitInfo {
+                    pr_number,
+                    commit_sha,
+                    authors,
+                });
+            }
+        }
+    }
+
+    // Fallback: find the commit that added the file
     let output = std::process::Command::new("git")
         .args([
             "log",