Fix exit code for call subcommand when tool execution fails

[Copilot]

The call subcommand was not returning proper exit codes when encountering execution errors (such as calling unknown tools). This made it impossible to use the tool effectively in CI pipelines and validation scripts.

Problem

Before this fix:

$ mcpt call unknown npx -y @modelcontextprotocol/server-filesystem ~
Error: Unknown tool: unknown
$ echo $?
0

The command would print the error message but exit with code 0, making it difficult to detect failures in automated environments.

Solution

Added proper error handling to check for execution errors (execErr) after calling MCP client methods and exit with code 1 when errors occur.

After this fix:

$ mcpt call unknown npx -y @modelcontextprotocol/server-filesystem ~
Error: Unknown tool: unknown
$ echo $?
1

Now the command correctly exits with code 1 for execution errors while maintaining code 0 for successful operations.

Changes Made

• Added 4 lines in cmd/mcptools/commands/call.go to check for execution errors and exit with code 1
• Added test case to verify error handling behavior
• All existing tests continue to pass
• Verified with integration testing

This enables proper use of mcptools in CI pipelines and validation workflows where non-zero exit codes are essential for detecting failures.

Fixes #53.

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