* refactor: consolidate number-checking utilities into shared helpers

Add _isFiniteNumber and _toFiniteNumber to utils/number.ts and export
from main-internal.ts. Replace scattered typeof+isFinite/isNaN patterns
with the shared utilities at 9 callsites across community and enterprise.

* refactor: strip verbose JSDoc from _isFiniteNumber/_toFiniteNumber

* refactor: add blank-string coercion note to _toFiniteNumber JSDoc

* refactor: introduce _clamp utility, replacing scattered Math.max/Math.min pairs

Adds `_clamp(value, min, max)` to `utils/number` and exports it from
`main-internal`. Replaces 19 identical two-call clamp patterns across
community and enterprise with a single, readable helper.

* fix build