Family: skolem — Zeros of linear recurrences (Skolem problem)

[roed-math]

One family: Zeros of linear recurrences (Skolem problem) (skolem) — P2, partial.

• Standard form: u_n = 0, u a linear recurrence
• Parent: exponential-diophantine

Contents: the registry entry and its docs/FAMILIES.md section.

References cited (the claim each one supports):

• Skolem1934 — the p-adic method behind the Skolem-Mahler-Lech theorem
• OuaknineWorrell2012 — survey: decidability known only up to order 4
• Bilu2022 — conditional decision procedure for simple recurrences

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