Add README, fix column deduplication in parser, remove .env from git

CHANGELOG.md

@@ -4,10 +4,20 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+---
+
+## [0.3.0] - 2026-06-03
+
+### Added
+- `README.md` — full project documentation: architecture overview, quick start, cache behaviour, persistence, configuration, exceptions, logging, and limitations
+
 ### Changed
-- `_meta.py` now reads version dynamically from installed package metadata via `importlib.metadata` instead of a hardcoded string
-- Bumped version to `0.2.0` in `pyproject.toml`
-- `CHANGELOG.md` restructured with `[0.2.0]` release section
+- `pyproject.toml` — bumped version to `0.3.0`
+- `parser.py` — `_extract_columns` now deduplicates column names while preserving order
+- `.gitignore` — added `.env` and `.env.*` to prevent accidental commit of environment files
+
+### Security
+- Removed `.env` from git tracking (`git rm --cached`)
 
 ---