Add native V-DMC safety core

[cicm4]

Summary

• add an independent C++20 V-DMC interoperability and safety core
• implement bounded V3C sample-stream, PTL/VPS, nested NAL, and conservative IDR-only HEVC validation
• provide public API scaffolding, CLI inspection/benchmarking, an installable CMake package, tests, sanitizers, and fuzzing
• add CI coverage plus provenance, licensing, and patent-boundary documentation

Current scope

This is the decoder-first safety boundary, not a complete MPEG V-DMC codec. Normative reconstruction and encoding remain unimplemented, and encode/decode fail with a structured unsupported-tool status before producing partial output.

Validation

• local Release: 38/38 tests
• local static and shared ASan/UBSan: 38/38 tests
• local deterministic sanitizer mutation smoke: 100,000 inputs
• remote Ubuntu GCC 13.3 Release: 38/38 tests
• remote Clang 18 ASan/UBSan: 38/38 tests
• remote seeded libFuzzer: 10,000 runs
• v14 Toolset 1 fixture inspected successfully; Toolset 0 rejected as expected
• installed-package downstream consumer passed
• CI-mode provenance, Markdown links, workflow YAML, and release-block checks passed

Release note

The repository remains intentionally release-blocked. Full normative decoding/encoding, optional video/GPU backends, Python bindings, CTC validation, and patent/distribution review are still required.

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