feat(backend): mount API routes + cookie-parser + CORS with credentials

- index.ts: mount /api/auth, /api/videos, /api/playlists; add cookie-parser; CORS with credentials + FRONTEND_URL env
- auth.middleware: read token from Bearer header OR od_token httpOnly cookie
- routes: auth (session/logout/me), videos (level-gated), playlists (CRUD + share management)
- deps: cookie-parser + @types/cookie-parser

backend/package-lock.json

@@ -9,6 +9,7 @@
       "version": "0.1.0",
       "dependencies": {
         "bcrypt": "^5.1.1",
+        "cookie-parser": "^1.4.7",
         "cors": "^2.8.5",
         "dotenv": "^16.4.5",
         "express": "^4.18.3",
@@ -19,6 +20,7 @@
       },
       "devDependencies": {
         "@types/bcrypt": "^5.0.2",
+        "@types/cookie-parser": "^1.4.10",
         "@types/cors": "^2.8.17",
         "@types/express": "^4.17.21",
         "@types/jsonwebtoken": "^9.0.6",
@@ -260,6 +262,16 @@
         "@types/node": "*"
       }
     },
+    "node_modules/@types/cookie-parser": {
+      "version": "1.4.10",
+      "resolved": "https://registry.npmjs.org/@types/cookie-parser/-/cookie-parser-1.4.10.tgz",
+      "integrity": "sha512-B4xqkqfZ8Wek+rCOeRxsjMS9OgvzebEzzLYw7NHYuvzb7IdxOkI0ZHGgeEBX4PUM7QGVvNSK60T3OvWj3YfBRg==",
+      "dev": true,
+      "license": "MIT",
+      "peerDependencies": {
+        "@types/express": "*"
+      }
+    },
     "node_modules/@types/cors": {
       "version": "2.8.19",
       "resolved": "https://registry.npmjs.org/@types/cors/-/cors-2.8.19.tgz",
@@ -901,6 +913,25 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/cookie-parser": {
+      "version": "1.4.7",
+      "resolved": "https://registry.npmjs.org/cookie-parser/-/cookie-parser-1.4.7.tgz",
+      "integrity": "sha512-nGUvgXnotP3BsjiLX2ypbQnWoGUPIIfHQNZkkC668ntrzGWEZVW70HDEB1qnNGMicPje6EttlIgzo51YSwNQGw==",
+      "license": "MIT",
+      "dependencies": {
+        "cookie": "0.7.2",
+        "cookie-signature": "1.0.6"
+      },
+      "engines": {
+        "node": ">= 0.8.0"
+      }
+    },
+    "node_modules/cookie-parser/node_modules/cookie-signature": {
+      "version": "1.0.6",
+      "resolved": "https://registry.npmjs.org/cookie-signature/-/cookie-signature-1.0.6.tgz",
+      "integrity": "sha512-QADzlaHc8icV8I7vbaJXJwod9HWYp8uCqf1xa4OfNu1T7JVxQIrUgOWtHdNDtPiywmFbiS12VjotIXLrKM3orQ==",
+      "license": "MIT"
+    },
     "node_modules/cookie-signature": {
       "version": "1.0.7",
       "resolved": "https://registry.npmjs.org/cookie-signature/-/cookie-signature-1.0.7.tgz",