Add CI workflow for automated build verification

[Copilot]

Implements GitHub Actions workflow to verify the software builds correctly using the documented installation steps from INSTALL.md.

Changes

• .github/workflows/build.yml: CI workflow that runs on push/PR to master/main
  • Installs build dependencies (g++, make, automake, autoconf, libtool, gfortran)
  • Generates configure script via make -f Makefile.git
  • Configures with ./configure --without-lapack
  • Builds with make -j 4
  • Includes explicit contents: read permission per security best practices

The workflow uses --without-lapack to avoid LAPACK/BLAS dependencies in CI while still validating the core build process.

Original prompt

Add a CI workflow. It should check that the software builds using the instructions in INSTALL.md

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