Configuration Sync

### Goal
Implement a sync mechanism that keeps ESPHome device configurations consistent
across multiple editing surfaces — primarily between the desktop app and a
hosted ESPHome instance (e.g. running inside Home Assistant).

### Context
Without sync, a user editing from their laptop risks diverging from or
overwriting the configuration managed by their ESPHome instance in Home Assistant.
Sync solves two distinct problems:

1. **Data safety** — Configurations are backed by a canonical source, so no
work is lost if the local machine is unavailable or replaced.
2. **Multi-surface editing** — A user can pick up on their laptop where they
left off in the HA-hosted ESPHome editor, and vice versa, without manual
export/import.

### Example Workflow
A user configures a new sensor on their laptop via the desktop app while away
from home. When they return, their ESPHome instance in Home Assistant reflects
the updated configuration automatically — ready to flash.

### Considerations
- Option to disable sync - some users might prefer their own sync option, like via git, rsync, etc
- Conflict resolution strategy when changes are made on both ends simultaneously
- Whether sync is push, pull, or bidirectional
- Authentication and secure transport between desktop app and HA/ESPHome instance
- Offline-first behavior — the desktop app should remain fully functional
without an active connection to the ESPHome instance