fix: use lstat instead of stat to detect symlinks in getFileMode

[FuturizeRush]

Summary

Replace stat() with lstat() in getFileMode() so symlinks are correctly detected and committed with Git mode 120000.

Bug

src/mcp/github-file-ops-server.ts:170 uses stat(), which follows symlinks and reports the target file's type. isSymbolicLink() on a stat() result always returns false.

const fileStat = await stat(filePath);   // follows symlink → sees target
// ...
} else if (fileStat.isSymbolicLink()) {  // always false with stat()
    return "120000";
}

Symlinks are committed as regular files (mode 100644) instead of symlinks (mode 120000).

Fix

stat() → lstat(). lstat() does not follow symlinks, so isSymbolicLink() correctly returns true.

Verified with Node.js

stat('/tmp/test-symlink').isSymbolicLink():  false  ← follows symlink
lstat('/tmp/test-symlink').isSymbolicLink(): true   ← sees symlink itself

Test plan

• tsc --noEmit passes
• Tested with real symlink: stat() returns false, lstat() returns true
• Regular files and directories unaffected (lstat() behaves identically to stat() for non-symlinks)