Align MCP port configuration to BrowserOS env-driven model (without changing default 3100)

[Copilot]

BrowserOS does not hardcode an MCP port and relies on environment configuration; this repo still had several fixed 3100 references that could drift from runtime settings. This PR aligns configuration surfaces and docs to the same env-driven port model while retaining 3100 as the intentional fallback/default.

• Runtime port model clarity

  • Clarified server/mcp-server.js behavior as environment-first port resolution with final fallback.
  • Kept existing precedence and default intact (MCP_SERVER_PORT → MCP_PORT → BROWSEROS_GUIDES_PORT → 3100).

• Container/config alignment

  • Updated docker-compose.yml to use BROWSEROS_GUIDES_PORT interpolation for:
    • MCP server published port mapping
    • inter-service MCP URL
    • MCP server environment assignment
  • This removes hardcoded compose wiring and keeps compose/runtime behavior consistent.

• Configuration discoverability

  • Added MCP host/port entries to .env.template so env-based port control is explicit and documented.

• Documentation synchronization

  • Updated README.md and QUICKSTART_MCP.md with explicit port override examples.
  • Added explicit port precedence note in Quickstart.
  • Added targeted comments in config.yml MCP sections indicating env-driven runtime resolution.

// server/mcp-server.js
const PORT =
  process.env.MCP_SERVER_PORT ||
  process.env.MCP_PORT ||
  process.env.BROWSEROS_GUIDES_PORT ||
  3100;

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/search/code
  • Triggering command: /usr/bin/python python scripts/check_browseros_ports.py (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)