feat(audio): Haus ambient sounds + YouTube player fix

WhiteNoise replaced with full ambient mixer:
- 6 categories: Noise, Rain, Nature, Places, Things, Animals
- 29 real ambient sounds from Haus (MIT licensed)
- Howler.js for playback with looping and per-sound volume
- Mix multiple sounds simultaneously
- Category tab navigation
- 300ms fade in/out for smooth toggling

MusicPlayer fixes:
- Removed origin param (causes issues behind reverse proxy)
- Added onError handler for YouTube errors
- Added onStateChange to track playing state
- Player container 1x1 opacity:0 instead of offscreen positioning

frontend/package-lock.json

@@ -8,6 +8,7 @@
       "name": "kira",
       "version": "0.1.0",
       "dependencies": {
+        "howler": "^2.2.4",
         "pixi-live2d-display": "^0.4.0",
         "pixi.js": "^7.4.3",
         "react": "^19.2.6",
@@ -15,13 +16,14 @@
       },
       "devDependencies": {
         "@tailwindcss/vite": "^4.1.6",
+        "@types/howler": "^2.2.13",
         "@types/react": "^19.2.14",
         "@types/react-dom": "^19.2.3",
         "@vitejs/plugin-react": "^6.0.1",
         "autoprefixer": "^10.4.20",
         "postcss": "^8.5.3",
         "tailwindcss": "^4.1.6",
-        "typescript": "~6.0.2",
+        "typescript": "^6.0.3",
         "vite": "^8.0.12"
       }
     },
@@ -871,6 +873,13 @@
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       "license": "MIT"
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+    "node_modules/@types/howler": {
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+      "resolved": "https://registry.npmjs.org/@types/howler/-/howler-2.2.13.tgz",
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+      "license": "MIT"
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     "node_modules/@types/offscreencanvas": {
       "version": "2019.7.3",
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@@ -998,9 +1007,9 @@
       "license": "MIT"
     },
     "node_modules/baseline-browser-mapping": {
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-      "resolved": "https://registry.npmjs.org/baseline-browser-mapping/-/baseline-browser-mapping-2.10.33.tgz",
-      "integrity": "sha512-bA6+tcSLpz2tIEdDXZPpPTIuxBcC4+w6SieaYyfigIa4h8GlFxbA17v22Vx3JUtuZQj9SgOsnbK+aTBzyDyEuw==",
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+      "resolved": "https://registry.npmjs.org/baseline-browser-mapping/-/baseline-browser-mapping-2.10.34.tgz",
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       "dev": true,
       "license": "Apache-2.0",
       "bin": {
@@ -1160,9 +1169,9 @@
       "license": "ISC"
     },
     "node_modules/electron-to-chromium": {
-      "version": "1.5.367",
-      "resolved": "https://registry.npmjs.org/electron-to-chromium/-/electron-to-chromium-1.5.367.tgz",
-      "integrity": "sha512-4Mk/mrynCNQ+atY40D3UpmhLWB6AHMbYMlIrPhHcMF6x0L7O0b052FCAsxw1LlaR++UFuNg3D/A6XCuGDa0guQ==",
+      "version": "1.5.368",
+      "resolved": "https://registry.npmjs.org/electron-to-chromium/-/electron-to-chromium-1.5.368.tgz",
+      "integrity": "sha512-7RckJJK4uESJF9PxvfMWd3TGqIiieUTG4HxnKaKuIpGbcr+r2ZEB3g2gAhCP3Fqm42vJSzLfgab9eva/C4/XVw==",
       "dev": true,
       "license": "ISC"
     },
@@ -1173,9 +1182,9 @@
       "license": "MIT"
     },
     "node_modules/enhanced-resolve": {
-      "version": "5.22.2",
-      "resolved": "https://registry.npmjs.org/enhanced-resolve/-/enhanced-resolve-5.22.2.tgz",
-      "integrity": "sha512-0rxICaFZ7NQho/sHely2bvOPRP0Eu2B0NZ9zM54YvRvWMn7jfz3DmnOZDR9LlXDdDcqntAVc6Hfy4gr/tdH/Ag==",
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       "dev": true,
       "license": "MIT",
       "dependencies": {
@@ -1512,6 +1521,12 @@
         "node": ">= 0.4"
       }
     },
+    "node_modules/howler": {
+      "version": "2.2.4",
+      "resolved": "https://registry.npmjs.org/howler/-/howler-2.2.4.tgz",
+      "integrity": "sha512-iARIBPgcQrwtEr+tALF+rapJ8qSc+Set2GJQl7xT1MQzWaVkFebdJhR3alVlSiUf5U7nAANKuj3aWpwerocD5w==",
+      "license": "MIT"
+    },
     "node_modules/inflight": {
       "version": "1.0.6",
       "resolved": "https://registry.npmjs.org/inflight/-/inflight-1.0.6.tgz",