v0.4.1 — json.Number tool argument decoding

Decode MCP tool arguments from raw wire bytes as json.Number, fixing:

• Raw _query tool rejecting Int GraphQL variables with float64 is not an int
• Int fields nested inside object-typed shortcut args (e.g. config.maxGapSeconds) hitting the same error
• Silent precision loss for integer values above 2^53 (e.g. Uint64 scalars)

Replaces per-arg coerceArgTypes coercion entirely. See #40.