Update from 1.10->1.11 Fails due to symlinks

I created a uv env from my local machine in a directory that also appears on /a0/usr. When the update happened, it failed to backup that directory because of the symlinks, so the update failed. Stack trace: [update_1.11_error.txt](https://github.com/user-attachments/files/27308990/update_1.11_error.txt) Claude analysis: ``` You trigger an A0 update 2 self_update_manager.py creates a rollback git stash 3 It tries to ZIP /a0/usr/ as a backup before making any changes 4 os.walk() reaches /a0/usr/workdir/reachy-mini-mcp/.venv/bin/ 5 Tries to add python to the ZIP → [Errno 2] No such file or directory 6 Exception → rollback triggered → update aborted every time That path does not exist inside the Docker container, so every symlink in .venv/bin/ is dangling. Python's zipfile.write() tries to follow the symlink to read the file and immediately fails. ``` Request: The create_usr_backup() function should skip broken symlinks gracefully as any broken symlink anywhere in /usr/workdir will block all future updates.