refactor: extract dereference and validate steps into controller modules

[adwk67]

Summary

• Extract the first two pipeline stages (dereference and validate) from the monolithic hdfs_controller.rs into controller/dereference.rs and controller/validate.rs
• Merge dereferenced fields (hdfs_opa_config) into ValidatedCluster, matching the pattern established in hive (#707) and hbase (#757)
• Replace image_base_name / pkg_version parameters with compile-time constants inside validate_cluster()

Test plan

• cargo clippy --all-targets — zero warnings
• cargo test — all 63 tests pass
• kuttl smoke tests

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