Fix BC MCP proxy to target current MCP server endpoint

[DmitryKatson]

Summary

The Business Central MCP proxy samples (Python bc-mcp-proxy and .NET BcMCPProxy) currently fail with HTTP 400 Bad Request as soon as they try to talk to Business Central, even when device-code sign-in succeeds and the Azure app registration is configured exactly as documented.

Root cause: Microsoft moved the BC MCP server. The proxies still call the old preview URL pattern, which BC no longer accepts.

	Old (broken)	Current (fixed)
URL	https://api.businesscentral.dynamics.com/v2.0/<env>/mcp	https://mcp.businesscentral.dynamics.com
Routing	environment in path, Company header only	TenantId, EnvironmentName, Company HTTP headers
OAuth scope	https://api.businesscentral.dynamics.com/.default	https://mcp.businesscentral.dynamics.com/.default

This matches the official guidance in Connect to Business Central MCP server with non-Microsoft clients and the connection string emitted by the Model Context Protocol (MCP) Server Configurations page in BC.

Changes

• samples/BcMCPProxyPython/bc_mcp_proxy/config.py — update base_url and token_scope defaults
• samples/BcMCPProxyPython/bc_mcp_proxy/proxy.py — drop /v2.0/<env>/mcp path suffix, add TenantId / EnvironmentName headers
• samples/BcMCPProxyPython/README.md — update parameter table defaults to match
• samples/BcMCPProxy/Models/ConfigOptions.cs — update Url and TokenScope defaults
• samples/BcMCPProxy/Runtime/MCPServerProxy.cs — same URL/header changes for the .NET proxy

Test plan

Verified end-to-end against a sandbox BC environment:

• Device-code sign-in succeeds and acquires a token for the mcp.businesscentral.dynamics.com resource
• MCP initialize handshake completes against mcp.businesscentral.dynamics.com (HTTP 200, server identifies itself as Microsoft Dynamics 365 Business Central v28.0)
• tools/list returns the BC dynamic tools (bc_actions_search, bc_actions_describe, bc_actions_invoke)
• bc_actions_search returns matching action names
• bc_actions_describe returns the action schema
• bc_actions_invoke on List_Customers_PAG30009 returns real CRONUS customer data (3 of 5 records)
• bc_actions_invoke on List_Items_PAG30008 returns real CRONUS item data (3 of 80 records)

Existing app registrations that already have Dynamics 365 Business Central → user_impersonation (delegated) continue to work — no Azure changes are required for end users.

Reproduction

Before this PR (with valid app registration and successful device-code sign-in):

INFO:bc_mcp_proxy:Connecting to Business Central MCP endpoint at https://api.businesscentral.dynamics.com/v2.0/Production/mcp
INFO:httpx:HTTP Request: POST https://api.businesscentral.dynamics.com/v2.0/Production/mcp "HTTP/1.1 400 Bad Request"

After this PR:

INFO:bc_mcp_proxy:Connecting to Business Central MCP endpoint at https://mcp.businesscentral.dynamics.com
INFO:httpx:HTTP Request: POST https://mcp.businesscentral.dynamics.com "HTTP/1.1 200 OK"
DEBUG:bc_mcp_proxy:Connected to remote MCP server (protocol 2025-11-25)

Notes for maintainers

• The Python sample's pyproject.toml version is unchanged (0.1.2). Once this PR is merged, the package will need a version bump and a PyPI release so end users get the fix without rebuilding from source.
• The BcMCPProxy.exe published artifact will likewise need a rebuild.