feat(player): webview audio backend for platforms without a native one

Adds WebviewAudioBackend, used on non-Linux/non-Android targets (e.g.
Windows) where there is no libmpv/ExoPlayer. Instead of decoding, it
emits a WebviewAudioLoad event with the stream URL; a frontend <audio>
element (WebviewAudioAdapter + webviewAudio service) plays it and reports
state/position back through the existing player_report_* round-trip, so
the Rust PlayerController stays the single source of truth. Play/pause/
seek reach the element via the existing ControlCommand event.

All video already renders in the webview on every platform, so this
completes audio-only playback for Windows (video via WebView2, audio via
<audio>). Pure Rust + Tauri events, so it still cross-compiles from Linux.

Regenerates bindings.ts (adds webview_audio_load; also carries the
equalizer EQ bindings).

TRACES: UR-003, UR-004, UR-005 | DR-004

src/lib/api/bindings.ts

@@ -173,6 +173,16 @@ async playerSetAudioSettings(settings: AudioSettings) : Promise<AudioSettings> {
 async playerGetAudioSettings() : Promise<AudioSettings> {
     return await TAURI_INVOKE("player_get_audio_settings");
 },
+/**
+ * The built-in equalizer presets and their per-band gain curves (dB), for the
+ * settings UI. The curve numbers are domain data defined by the band layout,
+ * so the frontend reads them here rather than encoding them.
+ * 
+ * TRACES: UR-027 | DR-030
+ */
+async playerGetEqPresets() : Promise<([EqPreset, number[]])[]> {
+    return await TAURI_INVOKE("player_get_eq_presets");
+},
 async playerSetVideoSettings(settings: VideoSettings) : Promise<VideoSettings> {
     return await TAURI_INVOKE("player_set_video_settings", { settings });
 },
@@ -1570,7 +1580,16 @@ normalizeVolume: boolean;
 /**
  * Target volume level for normalization
  */
-volumeLevel: VolumeLevel }
+volumeLevel: VolumeLevel; 
+/**
+ * Enable the graphic equalizer. When false, no EQ filter is applied.
+ */
+equalizerEnabled?: boolean; 
+/**
+ * Per-band gains in dB, one per [`EQ_BANDS`]. Normalised to 10 entries and
+ * clamped to [`EQ_GAIN_MIN`, `EQ_GAIN_MAX`] via [`Self::with_equalizer_normalised`].
+ */
+equalizerBands?: number[] }
 /**
  * Response for audio track switching operations
  */
@@ -1746,6 +1765,14 @@ export type DownloadVideoRequest = { itemId: string; userId: string; filePath: s
  * Enhanced response with pre-computed stats
  */
 export type DownloadsResponse = { downloads: DownloadInfo[]; stats: DownloadStats }
+/**
+ * Built-in equalizer presets. A preset *is* a gain curve defined by the band
+ * layout above (a domain concept), not a mere label — the curve numbers live
+ * in Rust so the frontend never encodes the taxonomy.
+ * 
+ * TRACES: UR-027 | DR-030
+ */
+export type EqPreset = "flat" | "rock" | "pop" | "jazz" | "classical" | "bassBoost" | "trebleBoost" | "vocal"
 /**
  * Genre
  */
@@ -2356,7 +2383,19 @@ export type PlayerStatusEvent =
  * or remote so they can pause/play/seek/stop the webview element.
  * `playerEvents.ts` routes this to the active PlayerAdapter via the facade.
  */
-{ type: "control_command"; action: string; position: number | null }
+{ type: "control_command"; action: string; position: number | null } | 
+/**
+ * Ask the frontend webview `<audio>` element to load and play a stream.
+ * 
+ * Emitted by `WebviewAudioBackend` on platforms with no native audio
+ * backend (e.g. Windows): audio-only playback is rendered by an `<audio>`
+ * element in the webview, mirroring how all video already renders through
+ * the webview `<video>`. The element then reports its state/position back
+ * through the `player_report_*` commands, so the Rust controller stays the
+ * single source of truth. Subsequent play/pause/seek/stop reach the element
+ * via `ControlCommand`.
+ */
+{ type: "webview_audio_load"; url: string; media_id: string | null; position: number; autoplay: boolean }
 /**
  * Result of creating a playlist
  *