safe-bash: add `factor` (integer factorization)

[kamilio]

Missing: factor. No prime factorization helper.

Behavior: GNU factor [NUMBER…] → N: p q r. Read numbers from args or stdin. Cap the magnitude (or use bounded BigInt with a work budget) so a large input cannot burn the CPU budget; reject values above the cap with a clear error.

From the safe-bash command gap analysis (2026-09-08). Sandbox constraints apply: bounded input/CPU/memory, VFS-only paths, cooperative cancellation, no host process/network beyond the existing curl authorizer.

[kamilio]

Implemented and verified on remote main at 73cdc99. Read the full GNU 8.30 factor utility and token reader. Adds exact bounded integer factoring for 0..4294967295, with a configurable lower ceiling and explicit rejection above it, as permitted by this issue; args/stdin, invalid-operand continuation, raw-byte/NUL cases, limits and cancellation are covered. Exposes all three factories, default registration and root/scoped Node/browser subpaths. Author126, independent91 and public4 cases pass; native fixtures distinguish exact comparisons from deliberate cap/banner qualifications. Full npm test/lint/final build/types/archive/package lint and22 fresh packed profiles pass; actual saved VFS scripts and terminal output inspected. See packages/safe-bash/docs/FACTOR.md for all bounds/qualified differences. Actual publication is monitored while work continues to #683.