docs: seed CHANGELOG.md (Keep-a-Changelog format)

CHANGELOG.md

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+<!--
+SPDX-License-Identifier: MPL-2.0
+SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath)
+-->
+
+# Changelog
+
+All notable changes to `docmatrix` will be documented in this file.
+
+This file is generated from conventional commits by the
+[`changelog-reusable.yml`](https://github.com/hyperpolymath/standards/blob/main/.github/workflows/changelog-reusable.yml)
+workflow (`hyperpolymath/standards#206`). Adopt the workflow in this repo's CI to keep this file in sync automatically — see
+[`templates/cliff.toml`](https://github.com/hyperpolymath/standards/blob/main/templates/cliff.toml)
+for the canonical config.
+
+The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/);
+this project aims to follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+
+- feat(crg): add crg-grade and crg-badge justfile recipes
+- feat: add k9iser.toml and generate K9 contracts
+- feat: add stapeln.toml container definition
+- feat: deploy UX Manifesto infrastructure
+- feat: replace Tauri with Gossamer — gossamer-rs backend
+- feat: Gossamer migration — RuntimeBridge, gossamer.conf.json, Tauri→Gossamer conversion
+- feat: add CLADE.a2ml — clade taxonomy declaration
+- feat: add mirror.yml workflow for GitLab/Bitbucket mirroring
+- feat: absorb docmatrix FFI extras from zig-ffi monorepo
+- feat: customize fuzz target with repo-specific logic
+
+### Fixed
+
+- fix(ci): bump a2ml/k9-validate-action pins to canonical (standards#85) (#18)
+- fix(ci): sync hypatia-scan.yml to canonical (kill cd-scanner build drift) (#17)
+- fix(ci): adopt canonical hypatia-scan.yml (env.HOME/scanner-layout + Comment-step gate) (#16)
+- fix(ci): Phase-2 fleet submission must not fail the security gate (#15)
+- fix(ci): hypatia-scan workdir (${{ env.HOME }} resolves empty) (#14)
+- fix(ci): hypatia-scan.yml -- pass GITHUB_TOKEN, use --exit-zero (hyperpolymath/hypatia#213) (#9)
+- fix(ci): bump erlef/setup-beam SHA for ubuntu24 runner support (#10)
+- fix(ci): repair YAML block-scalar in workflow-linter Check Permissions step (#11)
+- fix(ci): move secret-scanner Cargo.toml gate from job-level if: to step-level (#12)
+- fix: correct test compilation errors and achieve passing status
+
+### Changed
+
+- refactor: migrate 6SCM → 6A2 (.scm → .a2ml format)
+
+### Documentation
+
+- docs: substantive CRG C annotation (EXPLAINME.adoc)
+- docs: add EXPLAINME.adoc — prove-it file backing README claims
+- docs: add SECURITY.md for vulnerability reporting
+- docs: add checkpoint files for state tracking
+- docs: rename to DocMatrix
+
+### CI
+
+- ci(rust): convert rust-ci.yml to thin wrapper (standards#174) (#22)
+- ci: redistribute concurrency-cancel guard to read-only check workflows (#20)
+- ci(secret-scanner): drop duplicate --fail from trufflehog extra_args (#8)
+- ci: bump actions/upload-artifact SHA to current v4 (#7)
+- ci: SHA-pin hyperpolymath validate-actions in dogfood-gate
+
+## Pre-history
+
+Prior commits to this file's introduction are recorded in git history but not formally classified into Keep-a-Changelog sections. To backfill, run `git cliff -o CHANGELOG.md` locally using the canonical [`cliff.toml`](https://github.com/hyperpolymath/standards/blob/main/templates/cliff.toml) — this is one-shot mechanical work.
+
+---
+
+<!-- This file was seeded by the 2026-05-26 estate tech-debt audit follow-up (Row-2 Phase 3); see [`hyperpolymath/standards/docs/audits/2026-05-26-estate-documentation-debt.md`](https://github.com/hyperpolymath/standards/blob/main/docs/audits/2026-05-26-estate-documentation-debt.md). -->