fix(azure): purge disks without body etags

[ruby-dlee]

Summary

• accept the existing stable disk uniqueId fallback when Azure omits a body ETag
• preserve exact resource ID, tags, uniqueId, and detached-state checks
• reject shared-disk attachments through managedByExtended at planning and deletion
• document that the pinned Disk Delete spec does not declare If-Match compare-and-swap semantics

Validation

• tests/run.sh tests/fm-azure-validation.test.sh
• tests/run.sh tests/fm-worker-lifecycle.test.sh
• bin/fm-lint.sh
• Python compile, shell syntax, and diff checks
• independent review clear