feat: OSMO backend integrations

[TrevorBasinger]

Summary

• add a first-class OSMO execution backend to Roar and route osmo workflow submit ... through the execution framework
• support product-path OSMO usage with roar run osmo workflow submit ..., roar osmo attach ..., roar osmo prepare-workflow ..., and roar osmo export-lineage-bundle
• prove the end-to-end path with live OSMO basic and Ray-on-OSMO smoke tests on the moved tests/backends/osmo harness

What Changed

• added roar.backends.osmo with backend config, command planning, submit normalization, host-side wait/query handling, output downloads, diagnostics capture, lineage-bundle export, ingestion, and attach support
• added OSMO CLI commands for attach, workflow preparation, and lineage-bundle export
• implemented workflow preparation for transparent OSMO usage, including runtime install wrappers and the standard roar-lineage / roar-fragments.json contract
• recorded OSMO receipts, query diagnostics, downloaded outputs, and reconstituted child lineage in local .roar/roar.db
• made git/file-context handling degrade cleanly when git is unavailable inside remote task images
• updated the OSMO harness to the moved paths, switched smoke workload images off Docker Hub where appropriate, and hardened bootstrap cleanup and image preloading
• added focused regression coverage for backend registration, planning, host execution, attach flows, workflow preparation, runtime bundle export, and smoke paths