Sounds play on flutter_soloud instead of three mpv players

SoundEngine (platform/audio) opens the device once (2 s after start,
or on the first sound), loads each synthesized sound into memory (no
temp files), plays overlapping voices and is disposed on window close,
before leaving the server. The SfxService interface and its callers
are unchanged; loudness matches the old mpv path (v^6). WAV only, so
no codec libraries are bundled and no build packages are needed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/pubspec.lock

@@ -153,6 +153,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "0.1.2"
+  file:
+    dependency: transitive
+    description:
+      name: file
+      sha256: a3b4f84adafef897088c160faf7dfffb7696046cb13ae90b508c2cbc95d3b8d4
+      url: "https://pub.dev"
+    source: hosted
+    version: "7.0.1"
   file_picker:
     dependency: "direct main"
     description:
@@ -227,6 +235,14 @@ packages:
     description: flutter
     source: sdk
     version: "0.0.0"
+  flutter_soloud:
+    dependency: "direct main"
+    description:
+      name: flutter_soloud
+      sha256: "1c297e52182c5e8fd447ae8430bf0b598445dc586e72863ceeef0416242b2ae8"
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.2.1"
   flutter_test:
     dependency: "direct dev"
     description: flutter
@@ -246,6 +262,14 @@ packages:
       url: "https://git.senkochan.moe/Foxyz/fox_utils.git"
     source: git
     version: "0.1.9"
+  glob:
+    dependency: transitive
+    description:
+      name: glob
+      sha256: "218aeb56050c714f62a3182775320dfa04602b55074873e24e31bbd39bda96fb"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.2.0"
   hive_ce:
     dependency: "direct main"
     description:
@@ -495,6 +519,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.1.0"
+  native_toolchain_c:
+    dependency: transitive
+    description:
+      name: native_toolchain_c
+      sha256: "90eaad8059ebc2004a63810a4696ea9acdb02473e47ed3b6b3bafb100ac77e31"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.19.5"
   objective_c:
     dependency: transitive
     description:
@@ -623,6 +655,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "7.0.0"
+  process:
+    dependency: transitive
+    description:
+      name: process
+      sha256: "4242ba3508d37e01808bdf71ad1d5bb93a8d671bf2e7450e6b1b353fb0808891"
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.0.6"
   pub_semver:
     dependency: transitive
     description:
@@ -786,14 +826,14 @@ packages:
       path: "../../packages/core"
       relative: true
     source: path
-    version: "1.1.2"
+    version: "1.2.0"
   sync_relay_server:
     dependency: "direct main"
     description:
       path: "../../packages/server"
       relative: true
     source: path
-    version: "1.1.2"
+    version: "1.2.0"
   synchronized:
     dependency: transitive
     description: