docs: add changelog for v0.3.0

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Source: https://github.com/getlumos/lumos/releases/tag/v0.3.0

Author: github-actions[bot]

src/content/docs/changelog/v030.md

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+---
+title: "LUMOS v0.3.0 - Enhanced Error Tracking & Multi-Language Support"
+description: "Release notes for LUMOS v0.3.0"
+date: 2025-12-08
+---
+
+## What's New in v0.3.0
+
+### 🎯 Source Location Tracking (#121)
+- **Precise Error Messages**: Type validation errors now show exact line:column location
+- **Better Developer Experience**: Find and fix issues faster with pinpoint accuracy
+- **Example**: `Undefined type 'Player' (at 2:5)` instead of generic errors
+
+### 🔄 Complete Enum Migration Generation (#122)
+- **Automatic Migration Code**: Generate full Rust `From` impls and TypeScript migration functions
+- **Schema Evolution Made Easy**: Handles variant additions, removals, and all variant types
+- **Smart Mapping**: Removed variants automatically map to sensible defaults with clear comments
+
+### 🚀 Language Server Protocol (LSP) Enhancements
+- **Context-Aware Completions (#120)**: Smarter autocomplete based on cursor position
+- **Document Formatting (#129)**: Format-on-save support for `.lumos` files
+- **Enhanced Diagnostics**: Better error detection and hover information
+
+### 🌍 Multi-Language Code Generation
+- **Seahorse Python (#56)**: Generate Python programs for Solana
+- **Go & Ruby Support**: Full code generation for Go and Ruby
+- **Unified Interface**: Use `--lang` flag for any target language
+
+### ⛓️ Solana Ecosystem Integration
+- **Metaplex Token Metadata (#58)**: Full compatibility with NFT standard
+- **Native Solana Support (#57)**: Generate programs without Anchor framework
+
+### 📊 Quality & Testing
+- **322 Tests Passing**: Comprehensive test coverage (120 new tests since v0.2.0)
+- **Zero Warnings**: All clippy lints resolved
+- **Cross-Language Compatibility (#117)**: Verified schema compatibility across languages
+
+## Installation
+
+```bash
+# Install or update CLI
+cargo install lumos-cli
+
+# Install or update LSP server
+cargo install lumos-lsp
+
+# Verify installation
+lumos --version  # Should show 0.3.0
+```
+
+## Crates Published
+
+- `lumos-core v0.3.0` - https://crates.io/crates/lumos-core
+- `lumos-cli v0.3.0` - https://crates.io/crates/lumos-cli
+- `lumos-lsp v0.3.0` - https://crates.io/crates/lumos-lsp
+
+## What's Next
+
+See [ROADMAP.md](https://github.com/getlumos/lumos/blob/dev/ROADMAP.md) for upcoming features.
+
+## Full Changelog
+
+See [CHANGELOG.md](https://github.com/getlumos/lumos/blob/dev/CHANGELOG.md#030---2025-12-09) for detailed changes.
+
+---
+
+**Compatibility**: Fully backward compatible with v0.2.x schemas
+**Support**: https://github.com/getlumos/lumos/issues
+**Documentation**: https://lumos-lang.org
+
+---
+
+**Links:**
+- [GitHub Release](https://github.com/getlumos/lumos/releases/tag/v0.3.0)
+- [Compare changes](https://github.com/getlumos/lumos/compare/bc18c0135e3228af2ead12e3598740bb61f67d02...v0.3.0)