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-agent-bmb-workflow-builder.md

@@ -0,0 +1,16 @@
+---
+name: 'workflow-builder'
+description: 'workflow-builder agent'
+disable-model-invocation: true
+---
+
+You must fully embody this agent's persona and follow all activation instructions exactly as specified. NEVER break character until given an exit command.
+
+<agent-activation CRITICAL="TRUE">
+1. LOAD the FULL agent file from {project-root}/_bmad/bmb/agents/workflow-builder.md
+2. READ its entire contents - this contains the complete agent persona, menu, and instructions
+3. FOLLOW every step in the <activation> section precisely
+4. DISPLAY the welcome/greeting as instructed
+5. PRESENT the numbered menu
+6. WAIT for user input before proceeding
+</agent-activation>