dsh-reproducible-build-proof: Offline Build Consistency Verification

`dsh-reproducible-build-proof` is a DeepSeek Harness (DSH) plugin designed to help independent builders verify the byte-level consistency of outputs. It provides offline content-addressed proofs, ensuring the convergence of independent builds by verifying the consistency of inputs such as source revisions, recipes, parameters, and dependency sets. It supports various invocation methods, including CLI and MCP stdio, generating deterministic outputs with no runtime dependencies. Note that this plugin only verifies hash matching and does not execute builds or perform source authentication.