fix(streaming): keep playback on native device, surface failures (#282)

[LargeModGames]

Summary

Fixes #282. Native streaming could silently fail and route audio to the official Spotify client (or 404 with NO_ACTIVE_DEVICE) with no feedback to the user.

• Routing: after selecting the spotatui device, current_playback_context still held the previous device, so is_native_streaming_active_for_playback returned false and start_playback fell through to the deviceless me/player/play (which Spotify routes to whatever device is active). Now clears the stale context on native selection (mirrors the non-native transfer branch) and adds a short last_device_activation grace window to the routing gate, so the first play stays on the chosen native device. Safe vs Spotatui "hijacking" Spotify playback device from Android. #254 — the poll re-derives is_streaming_active each cycle and the recovery handler is untouched.
• Notification: handle_player_events dropped PlayerEvent::Unavailable into the catch-all arm, so audio-key failures were completely silent. Now handled with a consecutive-failure counter (reset on Playing) that shows a status message, escalating after 3 consecutive failures.
• Docs: README note about the upstream error audio key 0 1 limitation.

Testing

• cargo fmt --all -- --check — clean
• cargo clippy -- -D warnings — clean
• cargo clippy --no-default-features --features telemetry -- -D warnings — clean
• cargo test — 239 passed; 0 failed
• cargo test --no-default-features --features telemetry — 226 passed; 0 failed

Additional notes

• The error audio key 0 1 decryption block itself is an upstream Spotify change (correlated with account age — newer accounts fail, pre-2020 typically work) that affects all librespot-based clients (vanilla librespot #1649, spotify-player #910, go-librespot) and cannot be fixed in-app; librespot v0.8.0 is already the latest. This PR makes the failure visible and keeps playback on the device the user chose — it does not (and can't) restore audio for blocked accounts.
• Manual check (on an unaffected account): with the official Spotify app open, press d, select spotatui, and play — playback stays local instead of leaking to the official client.
• Possible follow-up: the NativePlaybackRoute::ContextApi path still targets me/player/play?device_id=… once native_device_id is known; out of scope here.