Config/ops: migrate runtime state paths to XDG conventions with compatibility

[mark-e-deyoung]

Summary

Adopt standard runtime/state path conventions for human and agent accessibility, while preserving compatibility.

Scope

• Move runtime pointer/state files from fixed /tmp/winebot_* locations to XDG-aligned defaults:
  • XDG_RUNTIME_DIR for volatile runtime pointers
  • XDG_STATE_HOME for persistent state where appropriate
• Keep explicit env overrides for all paths
• Add migration/compat fallback from legacy paths
• Update docs and diagnostics to show effective paths

Acceptance Criteria

• Runtime/state path locations are discoverable and configurable
• Backward compatibility with existing /tmp/winebot_* deployments is maintained
• Tests cover legacy fallback and XDG paths