Initial commit: BMAD framework + Story 1.1 Component Trait Definition

Features:
- BMAD (Build Modular AI-driven Development) framework setup
- BMM, BMB, CIS, Core modules configured
- Story 1.1: Component trait with error handling
- Workspace Cargo.toml with components crate
- 31 tests passing (19 unit + 12 doc tests)

Technical:
- Component trait with compute_residuals, jacobian_entries, n_equations
- ComponentError enum with thiserror
- JacobianBuilder for sparse matrix construction
- Object-safe trait supporting Box<dyn Component>
- Comprehensive documentation and examples

.agent/workflows/bmad-index-docs.md

@@ -0,0 +1,10 @@
+---
+name: 'index-docs'
+description: 'Generates or updates an index.md of all documents in the specified directory'
+---
+
+# index-docs
+
+Read the entire task file at: {project-root}/_bmad/core/tasks/index-docs.xml
+
+Follow all instructions in the task file exactly as written.