Refactor CasaTunes integration for Home Assistant 2026.9

[alphasixtyfive]

CasaTunes 0.2.0 modernizes the integration for Home Assistant 2026.9 and fixes API control and state-reporting bugs while preserving existing zone unique IDs and native search, TTS and doorbell actions.

• Remove the legacy Python client dependency and use one timeout-bounded, validated HTTP transport.
• Correct shuffle parameters, repeat support, buffering states and playback-position timestamps.
• Respect actual source capabilities, enabled sources and relative/fixed volume settings.
• Publish complete poll snapshots, cache metadata, and handle removed/new zones.
• Isolate grouping to a single server and refresh state before group cleanup.
• Update discovery and service registration; add address reconfiguration and redacted diagnostics.
• Add power-command debug logging, regression tests and current CI validation.

Validation: 57 tests passed against Home Assistant 2026.9.1; Ruff, Hassfest and HACS validation passed. Verified on CasaTunes 5.00.260818 after a Home Assistant restart: existing zone entities, power-on, source selection, mute, shuffle, repeat, media browsing and diagnostics. Other command paths are covered by automated tests; no destructive queue/group or audible TTS tests were performed on the live household system.

Requires Home Assistant 2026.9 or newer. Restart Home Assistant after installing. Generic URLs, URL announcements and the standard queue-next option are not supported; use CasaTunes media IDs and the native TTS/doorbell actions.

This release does not claim to resolve server-side idle shutdowns. Keep-on workarounds remain separate user automations.