microagent v0.19.0

Fixed

• Create the default configuration atomically and leave an existing file untouched.
• Treat a repeated edit as already applied instead of changing the file again.
• Serialize concurrent stderr notes and MCP handshake arena writes.
• Record benchmark run timestamps in UTC regardless of the host timezone.
• Check repeated tool-call IDs and names by buffer identity, avoiding a
  platform-dependent allocator-capacity assertion on macOS.
• Build with Homebrew's Zig layout on macOS by discovering the compiler's
  library directory instead of assuming it sits beside the executable.