fix: previews follow the app volume; volume bar fill always accent

The preview backend never received a volume — clips played at the crate
default (0.7) regardless of the slider, even muted. The session now sets
the preview volume from the app store (mute → 0) before the first load and
mirrors it live while the modal is open; the debug overlay's PREVIEW row
exposes the backend's resting volume as proof.

The player-bar volume (and fallback seek) fill is now always the accent
color — matching the waveform scrubber's played region — stepping up to
the hover shade on hover instead of white-until-hover.

Also syncs package-lock to the soulstream name + alpha version.

package.json

@@ -2,7 +2,7 @@
   "name": "soulstream",
   "version": "0.1.0-alpha.1",
   "type": "module",
-  "description": "SoulStream \u2014 music player, downloader and streamer for the Soulseek network",
+  "description": "SoulStream — music player, downloader and streamer for the Soulseek network",
   "scripts": {
     "dev": "vite",
     "build": "vite build",