docs(releases): add missing PRs to v0.16.1 release notes

[itomek]

Summary

• Add Process Analyst Agent (feat(cpp): Process Analyst Agent with LemonadeClient and background monitoring #426) section to v0.16.1 release notes — covers the ProcessAgent C++ class, 7 diagnostic tools, LemonadeClient C++ class, and SystemMonitor background monitoring
• Add MCP Config Stacking & Tool Display Naming (Fix MCP config stacking and tool display naming #477) section — covers two-level config loading and the tool_name (server) display format
• Update Full Changelog from 6 to 8 commits with entries for both PRs

Test plan

• Review rendered MDX in docs preview
• Verify all tool names and class names match source code

Closes #426, #477