Add Maestro BPMN validation fixtures

[gozhang2]

Summary

• Adds a public-safe synthetic Maestro BPMN validation corpus covering linear process, gateway/boundary error, Integration Service enrichment, and subprocess/multi-instance shapes.
• Adds a dependency-free fixture checker for BPMN parseability, UiPath extension/resource binding references, generated package metadata, Integration Service fields, and public-safety guardrails.
• Wires the checker into the Maestro BPMN maintenance suite and documents contributor/CI commands with a smoke eval task.

Validation

• bash skills/uipath-maestro-bpmn/.maintenance/check-validation-fixtures.sh -> passed (validation_fixture_projects=4 bpmn_files=4 errors=0)
• bash skills/uipath-maestro-bpmn/.maintenance/check-all.sh -> passed
• uv run ruff check skills/uipath-maestro-bpmn/.maintenance/check-validation-fixtures.py -> passed
• uv run ruff format --check skills/uipath-maestro-bpmn/.maintenance/check-validation-fixtures.py -> passed
• XML/JSON/YAML parse checks for new fixtures/tasks -> passed
• run_workspace_checks(kinds=auto) -> fmt passed for changed Python, tests passed; repo-wide lint failed on existing unrelated tests/ ruff issues
• Phase-N full gate run_workspace_checks(check_kinds=["fmt","lint","typecheck","test","test_web"]) -> failed on existing repo-wide tests/ ruff format/lint drift; pytest passed, typecheck/test_web skipped as expected

Notes

• Fixtures are synthetic and contain no raw exported BPMN, tenant data, connection IDs, folder keys, user names, local paths, or temporary mission notes.
• Draft PR opened for human review before merge.

[gozhang2]

Closed as duplicate/stale. The shared Maestro BPMN PR #616 now contains these validation fixtures plus the smoke-task schema repair commit; review should continue there.