fix: sanitize MCP names for OpenAI tool calls

Summary

• Fixes: MCP tools such as fs.read and nezha::server.exec are exposed unchanged as OpenAI function names, causing a 400 response because they do not match ^[a-zA-Z0-9_-]+$.
• Root cause: toolInfoFromDefinition copied the raw MCP name into schema.ToolInfo.Name even though that field is serialized as an OpenAI function name; the bridge already retains the raw name separately for MCP invocation.

Regression evidence

• Before: go test ./internal/einomcp -run TestToolInfoFromDefinitionSanitizesOpenAIToolName -count=1 exited 1

• After: go test ./internal/einomcp -run TestToolInfoFromDefinitionSanitizesOpenAIToolName -count=1 exited 0

Verification

• go test ./...
• go vet ./internal/einomcp
• test -z "$(gofmt -l internal/einomcp/mcp_tools.go internal/einomcp/mcp_tools_test.go)"

Scope

• 2 files changed, +58 / -9 lines