feat: Add companion WiFi CLI

[dz0ny]

This is a small PR that enables configuring wifi over CLI.

ref: #917

[Copilot]

Pull request overview

This PR adds persisted WiFi credentials to the companion_radio example and exposes them via the CLI rescue interface so WiFi can be reconfigured without recompiling firmware.

Changes:

• Extend NodePrefs with persisted wifi_ssid/wifi_pwd fields.
• Persist/load WiFi credentials in DataStore and use them during ESP32 WiFi startup.
• Add CLI rescue commands to set/get WiFi SSID/password and restart WiFi after updates.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
examples/companion_radio/NodePrefs.h	Adds persisted fields for WiFi SSID/password.
examples/companion_radio/DataStore.cpp	Saves/loads the new WiFi fields as part of prefs storage.
examples/companion_radio/MyMesh.cpp	Adds “effective WiFi creds” helpers, WiFi restart helper, and CLI rescue set/get commands.
examples/companion_radio/main.cpp	Uses persisted WiFi credentials (fallback to build-time) when starting WiFi on ESP32.

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