Fix Descope auth flow in remote-mcp-server-descope-auth demo

[mariamantsurova]

Align the demo with Descope Inbound Apps and the modern Workers/MCP setup:

• Use an Inbound App Client ID/Secret instead of the Project ID + Management Key. Rename env vars to DESCOPE_CLIENT_ID / DESCOPE_CLIENT_SECRET.
• Token exchange now uses the confidential-client form (application/ x-www-form-urlencoded with client_id + client_secret) against /oauth2/v1/apps/token.
• Request openid profile email scopes on /authorize so /userinfo works.
• Add nodejs_compat compatibility flag so the Worker builds.
• Update README + landing page: Inbound App creation via Agentic Identity Hub, user-information scope mapping, Streamable HTTP (/mcp) instead of SSE, corrected wrangler kv commands, and a troubleshooting table.
• Refresh Inspector screenshot.

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Latest commit: 578fe23

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