fix(connection): auto-reconnect until klipper is ready, drop retry button

[gmmcosta15]

Description

• Feature
• Bug fix
• Code refactor
• Documentation

ConnectionPage now shows only while Klipper/Moonraker is down. It keeps retrying on its own and returns to the main window when Klipper is ready. The only buttons left are Restart Klipper and Restart Firmware.

• Websocket: one retry timer every 3s with no cap, stopped only by an intentional disconnect.
• Klippy: server.info is polled every 2s in any non-ready state with no cap. The state signal is sent only when the state changes, and the tracked state is reset on reconnect and on notify_klippy_disconnected.
• Retry button removed from ConnectionPage.
• mainWindow: removed the duplicate klippy_state_signal connection.
• mainWindow: the automatic klipper service restart waits 15s in "disconnected", so a RESTART/SAVE_CONFIG or systemd's own restart (RestartSec=10) no longer triggers it.

Motivation

After #211 the page froze: the websocket gave up after 3 attempts, and the Klippy poll stopped after 60s, which is shorter than Klipper's 90s MCU connect window.

Tests

• Unit tests added for moonrakerComm, mainWindow and ConnectionPage.

[RobeMartins]

lgtm