Consume rheological models from rheomodel (1.1.0)

[marcocaggioni]

Removes the vendored model definitions from rheofit: the nine modules in
rheofit/models/ are now thin adapters that import equations, parameters,
bounds, the nesting ladder and citations from rheomodel. Only the fitting
hooks (initial_guess, seed_from_parent, fit_model) stay in rheofit;
_fitcore.py is untouched (_func = equation alias).

Also: adds rheopy-rheomodel>=0.1 to dependencies, bumps to 1.1.0
(public API unchanged), updates the README layout, docs/conf.py, and
both skill copies (new-model workflow now starts in rheomodel).

Verification

• all 9 model equations numerically identical old-vs-new (1e-12)
• all 9 models fit on the Carbopol PG flow curve: parameters, RedChi2
  and notes bit-identical at fast effort; tc + herschel_bulkley also
  identical at normal effort
• sphinx autodoc build clean (only pre-existing warnings from the
  skipped interactive-export step)

Note: rheopy-rheomodel is not on PyPI yet (trusted publisher not
configured), so installs/CI depending on it will fail until the v0.1.0
release publishes.