feat: add quality/transcoding options to live player (#6)

Manual quality profiles (source/1080p/720p/480p) in the player overflow
menu plus an honest/preparatory Auto contract: adaptive when the HLS
manifest exposes multiple levels, single-rendition automatic selection
otherwise.

- server: transcodeQualityProfiles service and qualityMode session option
- player: quality menu, persisted preference, live switch with rollback
- tests: npm test script and unit tests for quality profiles

package.json

@@ -6,7 +6,8 @@
     "main": "server/index.js",
     "scripts": {
         "start": "node server/index.js",
-        "dev": "node --watch server/index.js"
+        "dev": "node --watch server/index.js",
+        "test": "node --test"
     },
     "dependencies": {
         "@ffprobe-installer/ffprobe": "^2.1.2",
@@ -29,4 +30,4 @@
     "engines": {
         "node": ">=18.0.0"
     }
-}
+}