docs: seed CHANGELOG.md (Keep-a-Changelog format) (#18)

## Summary
Adds an initial `CHANGELOG.md` in Keep-a-Changelog format. Recent
commits are bucketed into Added/Fixed/Changed/Documentation/CI from
their conventional-commit prefixes.

Closes **Row-2 Phase 3** of the 2026-05-26 estate tech-debt audit chain
for this repo. The audit
([standards#197](hyperpolymath/standards#197))
flagged 180/279 repos missing CHANGELOG (65% gap).

## Adopting auto-regeneration
For ongoing auto-regeneration, adopt the
[`changelog-reusable.yml`](https://github.com/hyperpolymath/standards/blob/main/.github/workflows/changelog-reusable.yml)
workflow
([standards#206](hyperpolymath/standards#206))
in this repo's CI. Uses the canonical
[`templates/cliff.toml`](https://github.com/hyperpolymath/standards/blob/main/templates/cliff.toml).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

CHANGELOG.md

@@ -0,0 +1,52 @@
+<!--
+SPDX-License-Identifier: MPL-2.0
+SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell (hyperpolymath)
+-->
+
+# Changelog
+
+All notable changes to `befunge93-vault-cracker` 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: add Grade B test suite (6 targets)
+
+### Fixed
+
+- fix(ci): sync hypatia-scan.yml to canonical (kill cd-scanner build drift) (#9)
+- fix(ci): adopt canonical hypatia-scan.yml (env.HOME/scanner-layout + Comment-step gate) (#8)
+- fix(ci): Phase-2 fleet submission must not fail the security gate (#7)
+- fix(ci): hypatia-scan workdir (${{ env.HOME }} resolves empty) (#6)
+- fix(ci): hypatia-scan.yml -- pass GITHUB_TOKEN, use --exit-zero (hyperpolymath/hypatia#213) (#3)
+- fix(ci): bump erlef/setup-beam SHA for ubuntu24 runner support (#4)
+- fix(ci): move secret-scanner Cargo.toml gate from job-level if: to step-level (#5)
+
+### Documentation
+
+- docs: add post-audit status report for M5 sweep
+- docs(explainme): add EXPLAINME.adoc
+
+### CI
+
+- ci: bump actions/upload-artifact SHA to current v4 (#2)
+- ci(secret-scanner): drop duplicate --fail from trufflehog extra_args (#1)
+- ci: restore Dependabot security path + wire auto-merge
+
+## 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). -->