improve development authentication setup

- Replaced manual code commenting with environment variable controlled mock auth
- Added development env vars to VS Code launch.json for automatic mock authentication
- Removed unused LinkedIn provider import
- Authentication now automatically uses mock session when launched via VS Code debug
- Zero security impact on production (env vars only exist during debug sessions)

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.vscode/launch.json

@@ -9,6 +9,11 @@
             "type": "node",
             "request": "launch",
             "envFile": "${workspaceFolder}/.env",
+            "env": {
+                "USE_MOCK_AUTH": "true",
+                "MOCK_USER_ID": "109754742613069927799",
+                "MOCK_USER_NAME": "Nikola Derežić"
+            },
             "runtimeArgs": [
                 "run", // this is `run` from `npm run`
                 "dev" // this is `dev` from `npm run dev`