Family: fermat — Fermat equation

[roed-math]

One family: Fermat equation (fermat) — P1, solved.

• Standard form: x^n + y^n = z^n, n >= 3
• Parent: generalized-fermat
• Examples: x^4 + y^4 = z^4, x^n + y^n = z^n

Contents: the registry entry, its docs/FAMILIES.md section, its rows in the classification corpus, its solver and solver-layer tests.

References cited (the claim each one supports):

• Wiles1995 — the proof of Fermat's Last Theorem (semistable case)
• TaylorWiles1995 — the companion paper completing the proof

Independent of every other family PR: it needs only the registry backbone it is based on.

Part of the series that splits #1 into reviewable pieces:

1. 01-bibliography — packaging, docs, annotated bibliography
2. 02-parsing — equation strings to a term model
3. 03-registry — the YAML family registry (3 seed families)
4. 04-matchers — shape recognizers
5. 05-classify — the classification pipeline
6. 06-solvers — solver framework, two seed solvers, and the CLI
7. 07..09-backbone — the 23 parent families of the DAG, by depth
8. one PR per remaining family (38 of them, mutually independent)
9. 99-polish — restore the full doctests and tighten the invariants