Reconsider PR #850: Wrong Fix for a Potentially Invalid Use Case #929

References: PR #850, Issue #260

Rationale 1: charset=utf-8 is non-conformant

RFC 8259 §8.1 and IANA do not recognize charset as a valid parameter for application/json.

This might result in status 415 with strict servers.
csharp-sdk issue

Rationale 2: Non-ASCII tool names are spec-violating

The MCP spec and accepted SEP-986 both restrict tool names to [a-zA-Z0-9_\-.]. Non-ASCII characters like 天気予報 are outside this set (SHOULD, not MUST — but still discouraged).

Proposed Actions

1. Revert Content-Type header change
2. Add tool name validation at registration

Happy to submit a PR if maintainers agree.

@Kehrlann