[docs] switch generated docs to MkDocs

docs/index.md

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+# meanas
+
+`meanas` is a Python package for finite-difference electromagnetic simulation.
+It combines:
+
+- `meanas.fdfd` for frequency-domain operators, sources, waveguide modes, and SCPML
+- `meanas.fdtd` for Yee-grid timestepping, CPML, energy/flux accounting, and phasor extraction
+- `meanas.fdmath` for the shared discrete operators and derivations underneath both solvers
+
+This documentation is built directly from the package docstrings. The API pages
+are the source of truth for the mathematical derivations and calling
+conventions.
+
+## Recommended starting points
+
+- Use the [FDTD API](api/fdtd.md) when you need time-domain stepping, CPML, or
+  phasor extraction.
+- Use the [FDFD API](api/fdfd.md) when you need driven frequency-domain solves
+  or operator algebra.
+- Use the [Waveguide API](api/waveguides.md) for mode solving, port sources, and
+  overlap windows.
+- Use the [fdmath API](api/fdmath.md) when you need the lower-level finite-difference
+  operators or the derivation background shared across the package.
+
+## Build outputs
+
+The docs build generates two HTML views from the same source:
+
+- a normal multi-page site
+- a print-oriented combined page under `site/print_page/`
+
+If `htmlark` is installed, `./make_docs.sh` also writes a fully inlined
+`site/standalone.html`.