refactor(cmd): split main.go into cohesive files (under size gate)

[krisarmstrong]

Summary

• cmd/stem/main.go was 1532 lines — over the project >1200-line red flag. Split verbatim along functional seams into six new files in package main (no new packages, no import changes elsewhere, no logic changes).
• cmd_test.go was renamed to cmd_testmaster.go because Go treats *_test.go files as test files, which hid the package symbols from the non-test build.

Split

File	Responsibility	Lines
main.go	Constants, func main(), dispatchSubcommand(), printVersion(), printUsage()	263
cmd_reflect.go	reflectCmd, reflectorStatsLoop, flag parsing, license check, config build	226
cmd_testmaster.go	testCmd, parseTestFlags, createTestConfig, parseFrameSizes, license check	316
cmd_test_runners.go	Individual RFC-2544/Y.1564 runner funcs, printTestResult, printCSVResults	328
cmd_web.go	webCmd	51
cmd_tui.go	tuiCmd, tuiReflectMode, tuiTestMode	158
cmd_help.go	helpCmd, tutorialCmd, glossaryCmd, listTestsCmd	171
cmd_license.go	licenseCmd, displayLicenseStatus	111

Validation

go build ./...                          ✅ clean (pre-existing libpcap dup-lib warning only)
go vet ./cmd/stem/...                   ✅ clean
golangci-lint run ./cmd/stem/...        ✅ 0 issues
go test ./cmd/stem/...                  ✅ ok (0.124s)
check-file-size.sh | grep main.go       ✅ no output (no longer a red flag)

Notes

• All code moved verbatim — zero logic changes, zero renames.
• No compat aliases (pre-v1 no-compat law).
• New filenames follow the existing cmd_ underscore convention established by cmd_install_ca.go.

[github-actions]

License Compliance Report

All dependencies pass license compliance checks

Go Dependencies

• Unknown: 31 package(s)
• MIT: 26 package(s)
• BSD-3-Clause: 16 package(s)
• Apache-2.0: 11 package(s)
• BSD-2-Clause: 1 package(s)

npm Dependencies

See full report in workflow artifacts

Allowed Licenses: MIT, Apache-2.0, BSD-*, ISC, CC0-1.0, MPL-2.0
Forbidden: GPL, AGPL, SSPL (strong copyleft)