feat: add document revocation validator

[mxllv]

Closes #540
Closes #538
Closes #539
Closes #541

Summary:

• Adds a shared is_revoked helper under contract/src/module/revocation_check.rs
• Blocks submit and transfer handling when revoke:{hash} exists
• Adds unit tests for missing key, present key, and lookup failure

Validation:

• cargo test still fails because of pre-existing compile issues in unrelated contract modules

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