Fix: --tools alone falsely flagged as conflicting with --toolsets

[sebin]

Fixes #379.

Summary

getToolsetsFromCmd guards against passing both --tools and --toolsets at the same time. It does so by reading the --toolsets value with GetString and rejecting any value that is non-empty and not "default":

toolsetsFlag, _ := cmd.Flags().GetString("toolsets")
if toolsetsFlag == "" {
    toolsetsFlag, _ = cmd.Root().PersistentFlags().GetString("toolsets")
}
if toolsetsFlag != "" && toolsetsFlag != "default" {
    logger.Fatal("Cannot use both --tools and --toolsets flags together")
}

--toolsets is declared with default "all" in init.go. GetString returns the default when the operator has not passed the flag, so the check fires every time someone passes only --tools:

$ ./terraform-mcp-server --tools=search_providers
time="..." level=fatal msg="Cannot use both --tools and --toolsets flags together"

Change

Replace the value-based check with a pflag.Flag.Changed check. Changed is true only when the operator set the flag on the command line, which is precisely the condition the original check was reaching for. The intent (forbid passing both flags) is preserved; the false positive on the declared default goes away.

Diff is +8 / -5 in main.go and a new test file.

Verification

$ go build -o ./terraform-mcp-server ./cmd/terraform-mcp-server/

# Before
$ ./terraform-mcp-server stdio --tools=search_providers
level=fatal msg="Cannot use both --tools and --toolsets flags together"
# exit 1

# After
$ ./terraform-mcp-server stdio --tools=search_providers,get_provider_details
level=info msg="Enabled individual tools: [search_providers get_provider_details]"
Terraform MCP Server running on stdio

go test ./... passes (578/578).

Test plan

• TestToolsFlagAloneDoesNotConflictWithDefaultToolsets — passes only --tools, asserts the Fatal is not triggered (uses a logrus ExitFunc override so a Fatal call would be observable without exiting the test binary).
• TestToolsAndToolsetsTogetherTriggersFatal — locks the negative behavior down: passing both flags explicitly must still Fatal.
• go test ./... — 578 pass.
• Manual repro: ./terraform-mcp-server stdio --tools=search_providers now starts cleanly.