fix: remove legacy service-connection MCP field

[jamesadevine]

Summary

Remove the dead service_connection field from McpOptions and fix incorrect documentation claiming 1ES uses service connections for MCP routing. Both targets use MCPG — the field was parsed but never read.

Changes

• src/compile/types.rs: Remove dead service_connection field from McpOptions
• AGENTS.md: Remove service-connection: from MCP config docs
• prompts/create-ado-agentic-workflow.md: Fix 3 incorrect 1ES MCP claims
• prompts/update-ado-agentic-workflow.md: Fix target compatibility note

See analysis comment for full investigation.

Closes #233

[github-actions]

🔍 Rust PR Review

Summary: Looks good — clean dead-code removal with accurate documentation fixes.

Findings

✅ What Looks Good

• Backward-compatible serde removal: McpOptions does not carry #[serde(deny_unknown_fields)] (that attribute is only on NetworkConfig), so removing service_connection is silently safe — any existing front matter with service-connection: will simply be ignored by serde going forward, which is exactly the correct behavior.
• Confirmed dead field: The removed field has zero read-sites in the codebase. The service_connection references in common.rs are for ADO token acquisition (generate_acquire_ado_token, generate_copilot_ado_env, generate_executor_ado_env) — completely unrelated to McpOptions.
• Documentation accuracy: The prompt corrections correctly reflect the actual compiler behavior — both standalone and 1es targets generate MCPG configs via {{ mcpg_config }}, no service-connection MCP routing exists in either path.
• Scope is appropriately tight: 4 files, 13 changed lines, single well-defined concern. No unrelated churn.

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