Implement webOS adapter input, screen, and power control operations

[Staphylococcus]

Parent: #20

Phase: 1.1.x parity build-out, still no default adapter switch.

Goal:
Add webOS adapter write/control operations for the non-brightness calls currently performed through bscpylgtv.

Scope:

• Switch HDMI input via tv/switchInput.
• Power off via system/turnOff, preserving the existing power-state guard behavior where applicable.
• Turn screen off via the current tvpower endpoint.
• Turn screen on via the current tvpower endpoint.
• Support older screen on/off endpoint fallbacks where practical.
• Preserve structured errors for unsupported endpoints and webOS error responses such as substate mismatches.
• Keep webOS request details inside the adapter boundary.

Acceptance criteria:

• Mock websocket tests assert the exact request payloads.
• Screen on/off fallback behavior is tested.
• Existing screen, lifecycle, suspend, and shutdown policy semantics are not changed.
• The production adapter still defaults to bscpylgtv.
• The policy layer continues to call adapter-neutral TV operations.

Out of scope:

• OLED brightness write parity.
• Making webOS the default adapter.
• Multi-TV profile selection.
• Removing Python dependencies.