trellis v4.1.2

Formula parity: $round and $concat join the frozen core.

• $round(value, decimals = 0) coerces with Number() and rounds half up at 10^decimals, matching the kernel ExprEvaluator.
• $concat(...values) stringifies each value, with null and missing fields as '', matching the kernel.
• The formula conformance matrix now covers rounding (including default precision) and concatenation (including a missing field), both with canonical round-trip.

Published to npm as trellis@4.1.2.