chore: add initial changelog for v1.0.0

Author: aciceri

CHANGELOG.md

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+# 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/1.0.0/).
+
+## [Unreleased]
+
+## [1.0.0] - 2025-08-29
+
+### Initial Release
+
+This is the first stable release of cardano-nix. Prior to this version, the project did not follow semantic versioning or maintain a proper changelog.
+
+### Features
+
+This release provides NixOS modules and packages for the Cardano blockchain ecosystem:
+
+**Core Services:**
+
+- **cardano-node** - Cardano blockchain node service
+- **ogmios** - WebSocket API for Cardano integration
+- **kupo** - UTxO indexing service
+- **cardano-db-sync** - Database synchronization service
+- **blockfrost** - API service integration
+- **oura** - Event streaming service
+
+**Infrastructure:**
+
+- **HTTP proxy** with load balancing capabilities
+- **Monitoring stack** with Prometheus and Grafana
+- **Private testnet** support for development
+
+**Developer Tools:**
+
+- Comprehensive documentation with auto-generated API reference
+- Flake templates for common deployment scenarios
+- Pre-commit hooks and development environment
+- Binary cache integration via Hercules CI
+
+### Package Versions
+
+- cardano-node: 10.3.1
+- ogmios: 6.8.0
+- kupo: 2.11.0
+- blockfrost: 3.1.0
+- oura: 1.9.1
+
+### Notes
+
+- Conway era compatible
+- All services include NixOS modules with full configuration options
+- Documentation available at GitHub Pages
+- Licensed under Apache 2.0
+
+---
+
+_Starting from v1.0.0, this project follows semantic versioning and maintains a proper changelog for all releases._
+
+<!-- generated by git-cliff -->