Fix push command issues with draft comments

- Fix comment body being posted as temp file path instead of content
  - Use `--input <file>` with `-f body=@-` to read from stdin properly
- Fix crash when `new*.md` has local modifications
  - Use `git rm -f` to force removal even with uncommitted changes
  - This allows iterating on draft comments without committing

Fixes issue where `gh api -f 'body=@{temp_file}'` was being interpreted literally as the string "@/var/folders/..." instead of reading the file contents.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ryan-williams

src/ghpr/cli.py

@@ -1167,7 +1167,8 @@ def push(
                             'gh', 'api',
                             '-X', 'POST',
                             f'repos/{owner}/{repo}/issues/{number}/comments',
-                            '-f', f'body=@{temp_file}',
+                            '--input', temp_file,
+                            '-f', 'body=@-',
                             log=False
                         )
                         comment_id = str(result['id'])
@@ -1276,7 +1277,8 @@ def push(
         if new_comment_renames and not dry_run:
             # Remove old draft files and add new comment files
             for old_name, new_name in new_comment_renames:
-                proc.run('git', 'rm', old_name, log=False)
+                # Use -f to force removal even if there are local modifications
+                proc.run('git', 'rm', '-f', old_name, log=False)
                 proc.run('git', 'add', new_name, log=False)
 
             # Create commit message