audit(CCSDSPack): pre-tag repository and MCU API consistency cleanup

[Inczert]

Purpose

Final repository audit before creating the v2.1.0 tag.

This PR does not change CCSDS/ECSS wire-format algorithms or the package ABI. It does clarify public C++ headers and correct hosted-vs-MCU API visibility: hosted-only configuration APIs are no longer advertised on MCU, and the corresponding Manager configuration-loading code is MCU-guarded.

Release-state cleanup

• finalize v2.1 release notes for the qualified main commit
• convert the changelog from an unreleased candidate entry to 2.1.0
• record completed promotion and final-main CI gates
• point README CI badges at main
• refresh CCSDS/PUS/CUC compliance evidence from stale candidate/pending language
• update the CCSDS profile from the old 125-test/pending-hardware state to the qualified 134-test release evidence
• update the installed-consumer example from find_package(CCSDSPack 2.0) to 2.1
• clarify that physical/native v2.1 evidence corresponds to the same library implementation as the qualified release line

Redundant/stale files removed

• V2_TRANSITION_ROADMAP.md: completed and duplicated the release acceptance list
• docs/CROSSCOMPILE.md: pointer-only duplicate of docs/CROSSBUILD.md
• docs/EXECUTABLES.md: duplicated CLI documentation; its unique build controls were moved into docs/CLI.md
• docs/PRIV_HELPER.md: obsolete v2.0 staging-branch workflow

A current root CONTRIBUTING.md replaces the obsolete maintainer note.

Operational documentation fixes

• fix Docker instructions to require the exact release tag expected by the Dockerfile
• update Docker release example to v2.1.0
• use the current one-command arm64 validation runner in package docs
• guard the Jammy-specific aarch64 dependency helper so it cannot silently rewrite a newer Ubuntu host to 22.04 repositories
• remove unrelated arm64 architecture setup from the bare-metal ARM dependency helper

Compliance invariant

The audit preserves the existing claim boundary:

• CCSDS 133.0-B-2 Issue 2 + Editorial Change 2
• ECSS-E-70-41A PUS-A supported subset
• ECSS-E-ST-70-41C PUS-C supported subset
• supported CCSDS 301.0-B-4 basic numeric CUC subset

No standards-facing behavior is changed. Issue #166 remains an explicitly non-conformance-changing CUC performance follow-up.

Merge only after Linux (22.04/24.04/26.04), Windows, Doxygen, and Robustness are green on the final PR head.

Final pre-hardware re-audit (2026-10-09)

• audited 34 public headers, 27 implementation files, 46 test/example source/configuration files, current documentation, CI, package/toolchains, and markdown relative-link targets
• corrected stale raw-buffer, CRC-wrapper, umbrella-header, packet-size, and host/MCU API comments
• updated every example CMake package requirement to 2.1
• fixed the historical v1.2 release link and broken versionless docker/build_docker.sh
• distinguished earlier Pi/H755 successful runs from required fresh physical/native runs on the final post-audit release commit
• updated V2_TRANSITION_ACCEPTANCE_LIST.md and release notes to keep that hardware gate open
• removed the premature 2.1 changelog publication date

Hardware qualification: the prior H755 and Pi executions are historical evidence against the earlier implementation. PR #169 modifies MCU-facing API visibility and therefore requires a fresh exact-commit hardware run even though C11 protocol core and wire-format logic have not changed. Tagging is blocked until that evidence is recorded.

All changes must pass Linux (including Cortex-M compile/link), Windows, Doxygen, and Robustness CI on the final PR head before merge.