v0.5.0 — CatalogModel role extension

CatalogModel role extension. The Model Manager's per-row state (installed flag, in-flight loading flag, download progress) now flows through proper Qt roles on the catalog model instead of parallel QVariantMap / QVariantList snapshots rebuilt on every event. Same UX, lighter signal traffic on the hot path during model installs, and the foundation for the deferred custom-STT-path catalog work.

Added

• loading, progress, downloadable, managed roles on CatalogModel alongside name and installed. QML delegates bind directly to model.loading / model.progress; the previous voiceAgent.sttProgressMap[model.name] lookups are gone.
• CatalogStateProvider Protocol decouples CatalogModel from loaders and backends. The window-side _CatalogStateAdapter pulls live state from the loader + service so MainWindow no longer carries duplicate _active_items / per-item progress dicts.
• refresh_row(name) and refresh_progress(name) on CatalogModel. The narrow-role variant emits dataChanged with only [ProgressRole], keeping installed/loading-driven sibling bindings asleep between sub-second aria2 ticks.
• is_item_managed and is_item_downloadable on WhisperTranscriber and PiperTtsService. PiperTtsService also gains a new known_voice_names() classmethod that consolidates installed + cached unions as a single source of truth.
• sttInstalledCount / ttsInstalledCount Q_PROPERTYs on MainWindow. Replaces the QML-side countInstalled() JS helper that iterated sttCatalog/ttsCatalog on every ui_changed.

Changed

• ParallelItemLoader._finish_success no longer emits a synthetic terminal item_progress_changed. That frame existed only to keep the dropped *ProgressMap "busy" predicate honest; the refresh_row triggered by item_loading_changed(name, False) now drives the row back to idle through the adapter.

Removed

• MainWindow.downloads_changed / downloads_progress_changed signals and the matching sttCatalog, ttsCatalog, sttProgressMap, ttsProgressMap, sttDownloadingList, ttsDownloadingList properties. Per-row state now flows through CatalogModel's roles. The *DownloadingList properties had no remaining QML consumers.