Add contextual word-analysis prompts

[isomorphisms]

What this adds

A deliberately tiny design-time layer on top of the exact A2/A3 reducer.

• context_hints.py prints optional prompts for three caller-supplied capabilities: a renderable hyperbolic surface, Gromov/word-space analysis, and a finite-state action suitable for considering Krohn-Rhodes.
• reduce_with_context.py wraps the exact reducer without changing its reduction or evidence logic. JSON stays on stdout; optional prose goes to stderr.
• No prompt fires by default. A2/A3 are finite spherical types and the reducer does not pretend to infer hyperbolic geometry or semigroup structure.
• notes/krohn-rhodes.md records the key boundary: Krohn-Rhodes applies to finite transformation semigroups/automata, not to an isolated Coxeter word merely because it is a word.
• tests/test_context_hints.py checks capability gating, the August 26, 2026 design-time/LLM disclaimer, and the stdout/stderr boundary of the wrapper.

Cross-repository direction

The hyperbolic-render prompt names isomorphisms/indras-pearls as the intended renderer handoff. The receiving-side boundary is documented in isomorphismes/indras-pearls#2.

This PR is stacked on research/reflections-dynkin because it uses the A2/A3 reducer introduced there. It does not add general equality saturation, a Gromov implementation, a renderer, or a Krohn-Rhodes engine.