chore: add changelog and documentation updates

- Created a new `CHANGELOG.md` file to document all notable changes to the project, adhering to the Keep a Changelog format.
- Updated `CONTRIBUTING.md` to include instructions for building and previewing documentation using MkDocs.
- Added `mkdocs.yml` configuration for documentation generation, including navigation structure and theme settings.
- Enhanced various documentation files, including API reference, architecture overview, configuration reference, and runbook, to provide comprehensive guidance for users and developers.
- Included new sections in the README for changelog and documentation links, improving accessibility to project information.

CHANGELOG.md

@@ -0,0 +1,29 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [0.1.0] - 2025-02-20
+
+### Added
+
+- Telegram bot with python-telegram-bot v22 (polling, Application API).
+- Commands: `/start`, `/help`, `/set_phone`, `/import_duty_schedule`, `/pin_duty`.
+- Miniapp (calendar and duty list) served at `/app` with Russian and English (i18n).
+- FastAPI HTTP API: `GET /api/duties`, `GET /api/calendar-events`, `GET /api/calendar/ical/{token}.ics`.
+- Telegram initData validation for Miniapp; optional phone-based access (`ALLOWED_PHONES` / `ADMIN_PHONES`).
+- SQLite (default) / configurable DB; SQLAlchemy models, repository, Alembic migrations.
+- Duty-schedule import: two-step flow (handover time + JSON file); parser for meta.start_date and schedule[].duty.
+- Group duty pin: pin current duty message in group with time/timezone from `DUTY_DISPLAY_TZ`.
+- External calendar ICS URL support; personal ICS calendar by secret token.
+- Configuration via environment variables; full reference in docs/configuration.md.
+- Docker support (dev and prod compose); entrypoint runs migrations then app.
+
+### Security
+
+- Input validation and initData hash verification for Miniapp access.
+- Optional CORS and init_data_max_age; use env for secrets.
+
+[0.1.0]: https://github.com/your-org/duty-teller/releases/tag/v0.1.0