Add Futurehome house mode support (Modeswitch) + scene event entities

The Futurehome Modeswitch (Modusbryter) is a house-mode switch: its buttons
change the hub's mode (Home/Away/Sleep/Vacation), which is a hub-level Vinculum
concept broadcast via `evt.pd7.notify` (component "mode") — not a device
`scene_ctrl` event. That is why tapping it produced nothing in the device
message stream and the mapped scene sensor was stuck on `unknown`.

The add-on had no house-mode support at all. This adds it:

- Expose the current house mode as a `Mode` select on the Smarthub device.
  It reflects the current mode, updates in real time via `evt.pd7.notify`
  (with a 30s house-poll fallback), and can change the mode from Home Assistant
  via `cmd.pd7.request {cmd:"set", component:"mode", id:<mode>}` (matching the
  reference primefimp `ChangeMode`).
- Always publish the Smarthub hub device so the Mode select is available even
  without Thingsplex credentials; inclusion/exclusion tooling stays gated.
- Discover available modes from the Vinculum `mode` component, falling back to
  home/away/sleep/vacation.

Also improve genuine scene controllers: `scene_ctrl` now additionally exposes a
Home Assistant `event` entity so momentary button presses can drive automations
(the previous `Scene` sensor latched and could not react to repeated presses).
The sensor is kept for backwards compatibility (renamed "Scene (last value)").

Includes demo-mode support, README/CHANGELOG updates, and a version bump to
1.7.0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FuQAyPde4K57P2XMCKbFek

futurehome/config.yaml

@@ -1,6 +1,6 @@
 # https://developers.home-assistant.io/docs/add-ons/configuration#add-on-config
 name: Futurehome
-version: '1.6.2'
+version: '1.7.0'
 slug: futurehome
 description: Local Futurehome Smarthub integration
 url: 'https://github.com/adrianjagielak/home-assistant-futurehome'