Fix non-deterministic key ordering in generated MCPG config

[Copilot]

The MCPG config JSON embedded in compiled pipelines had non-deterministic key ordering, causing intermittent ado-aw check integrity failures where servers like safeoutputs and azure-devops would swap positions across runs.

Root cause: McpgConfig.mcp_servers and McpgServerConfig.{headers, env} were HashMap<String, _>. serde_json serializes HashMap in iteration order, which Rust's RandomState randomizes per-process — so the same source compiled to byte-different JSON.

Changes

• Switch the three serialized maps to BTreeMap<String, _> so JSON key order is sorted and stable.
• Update nonempty_map to convert HashMap → BTreeMap at the serialization boundary (input front-matter maps stay HashMap).
• Update try_add_user_mcp parameter and the accumulator in generate_mcpg_config.
• Update BTreeMap::from(...) constructions in extensions/safe_outputs.rs and tools/azure_devops/extension.rs.