Extract shared bundle metadata logic from coordinators

[guan404ming]

Related Issue

closes #69291

Why

NodeCoordinator, ExecutableCoordinator, and JavaCoordinator each carried verbatim copies of metadata validation, schema-version parsing, and root-path conversion, agreed for extraction in #68548 review.

How

• Add coordinators/_bundle_metadata.py with convert_roots, validate_schema_version, parse_metadata_mapping, extract_supervisor_schema_version, and ResolvedBundle
• Replace the duplicated implementations in all three coordinators with imports of the shared helpers
• Update one executable test asserting the now-unified metadata-rejection log event

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  Claude Code with Fable 5

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[jason810496]

Nice! Thanks for the consolidation.