chore: Bump version to 0.9.3

Release highlights:
- Removed CGO dependency for better portability
- Fixed critical MCP server bugs (path resolution, init tool)
- Improved Claude Code plugin documentation
- Enhanced MCP server configuration robustness
- All 91 tests passing

Major changes since 0.9.2:
1. CGO removal - Pure Go SQLite driver for easier installation
2. MCP init fix - Tool now correctly creates .beads in current directory
3. MCP path resolution - Auto-detects bd executable via PATH
4. Plugin docs - Better quickstart for Claude Code users
5. Config validation - Command names resolved via shutil.which()

Breaking changes: None
Migration: No action needed

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -957,7 +957,7 @@ See [examples/](examples/) for scripting patterns. Contributions welcome!
 
 ### Is this production-ready?
 
-**Current status: Alpha (v0.9.2)**
+**Current status: Alpha (v0.9.3)**
 
 bd is in active development and being dogfooded on real projects. The core functionality (create, update, dependencies, ready work, collision resolution) is stable and well-tested. However: