Keep showing last known values when the bike is out of range

Setup no longer depends on the bike being reachable. The coordinator is
built from an address and resolves the BLEDevice per connect attempt, so
a parked or switched-off bike loads the entry instead of raising
ConfigEntryNotReady and leaving every entity unavailable.

Parser state is persisted through helpers.storage.Store and restored
before the platforms are set up, so entities carry their last values and
the VIN on their first state write. What survives is a whitelist:
battery and EBM counters yes, motor and assist no - a restored speed
reading is indistinguishable from live data on a parked bike. The
connection switch position is restored too, so a restart no longer wakes
a bike the user deliberately disconnected.

Also fixes three defects found while building this:

- Store.async_delay_save debounces rather than throttles, so re-arming on
  every notification postponed the write for as long as the bike stayed
  connected and nothing reached disk except on a clean shutdown.
- establish_connection had no disconnected_callback, so a dropped link
  left _is_connected True: the connectivity sensor lied and the poll
  never retried.
- _connect read self._client back across the 200ms handshake, which a
  concurrent teardown could clear underneath it.

Connecting now starts on the bike's advertisement instead of the next
poll tick, and an unreachable bike says why - distinguishing "switched
off" from "seen only by a passive proxy that cannot connect".

Renames the connection switch to Auto-connect and drops the hardcoded
English name on the connectivity sensor, which had been defeating its
translation key.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FyabWZzd7HoLpyBwEa5Zzh

README.md

@@ -49,6 +49,10 @@ This integration provides real-time monitoring of your E-Bike through Bluetooth
 - **Range** (km)
 - **Light Status**
 
+### Diagnostics
+- **Last Seen** (Timestamp) - When the bike last sent data, so you can tell how fresh the values are
+- **Signal Strength** (dBm) - disabled by default
+
 ### Device Information
 The integration automatically retrieves and displays:
 - **Serial Number** (VIN) - 17-character bike serial number
@@ -115,6 +119,19 @@ The integration will automatically discover iWoc and HUS devices in range via Bl
 - Some sensors may show "Unknown" until the bike sends that specific data
 - Check if the bike is actively transmitting data (try riding or using the display)
 
+### Values after a Home Assistant restart
+
+The integration keeps working when the bike is switched off or out of range:
+
+- Counters and battery values (odometer, trip distance, range, state of charge,
+  remaining energy, light) are stored and shown again after a restart
+- Momentary readings (speed, motor temperature, assist level, battery current)
+  are **not** restored and show "Unknown" until the bike connects again — a
+  stale speed reading would look like live data from a parked bike
+- Use **Connected** and **Last Seen** to tell live data from last known values
+- The connection switch keeps its position across restarts, so a bike you
+  deliberately disconnected is not woken up again by a Home Assistant restart
+
 ### Connection Switch
 
 - **To disconnect**: Turn off the "Connection" switch in Home Assistant