Add a complete four-phase pipeline for testing Modelica libraries via
Base Modelica and Julia:

1. Export – instantiate models to .bmo via OMJulia (src/export.jl)
2. Parse  – create ODEProblem via BaseModelica.jl (src/parse_bm.jl)
3. Simulate – solve with Rodas5P from DifferentialEquations.jl (src/simulate.jl)
4. Compare – validate against MAP-LIB reference CSVs with configurable
             rel/abs tolerances; generate interactive Dygraph diff pages (src/compare.jl)

Top-level `main()` and `test_model()` orchestrate the full pipeline and
produce an HTML summary report (src/pipeline.jl, src/report.jl).

Also includes:
- CI workflow: add OpenModelica setup, omc-version matrix, sanity check
  step against MSL ChuaCircuit, and artifact upload
- Project.toml: add dependencies (BaseModelica, DifferentialEquations,
  ModelingToolkit, OMJulia, ZMQ, etc.)
- assets/: bundle Dygraph JS/CSS and an HTML diff template
- README: add usage docs and MSL v4.1.0 example
- .gitignore: exclude generated logs, CSVs, HTMLs, and result directories

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>