Create initial CHANGELOG.md

[msto]

Source: Expert Software Review (2026-02-17) — Software Durability

Description

The repository has no CHANGELOG.md despite:

• The publish workflow generating changelogs with git-cliff (publish.yml:125-145)
• The CLAUDE.md referencing CHANGELOG.md updates as part of the documentation maintenance checklist

Acceptance Criteria

• CHANGELOG.md exists at repository root
• Contains entry for 0.1.0 release
• Format is compatible with git-cliff's expected structure

Notes

Suggested content:

# Changelog

All notable changes to this project will be documented in this file.

## [0.1.0] - 2025-XX-XX

Initial release.

- `Metric` base class for type-validated delimited file models
- `MetricWriter` context manager for writing metrics to files
- Delimited list support (`list[T]` fields)
- Counter pivot table support (`Counter[StrEnum]` fields)
- Empty field handling (empty string -> None for Optional fields)
- UTF-8 BOM handling

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Issue ID: ISS-004
Created from: agent_notes/issues/issues_2026-02-17_fgmetric_review.md