fix(cli): default to text format when --format is omitted

[dmchaledev]

Problem

The tool's headline command — the very first example in the README and the npx one-liner — crashes for every user:

$ npx @hailbytes/sbom-diff old.json new.json
Error: Unsupported format: old.json
    at renderReport (dist/reporter.js:11:24)
    at main (dist/cli.js:30:17)

Root cause

In src/cli.ts the --format value was resolved with:

const formatArg = args.find(a => a.startsWith('--format='))?.split('=')[1]
  ?? args[args.indexOf('--format') + 1];

When --format is absent, args.indexOf('--format') returns -1, so args[-1 + 1] → args[0] — the first file path — gets used as the format. renderReport then throws on the unknown format.

So the documented default usage (text output, no flag) was completely broken; only the explicit --format=json / --format markdown forms worked.

Fix

• Extract argument parsing into a pure, unit-tested parseArgs helper (src/args.ts).
• Default to text when --format is omitted.
• Handle both --format json and --format=json, and consume the space-separated value so it isn't mistaken for a positional file argument (this also makes flag-before-files ordering work).
• Validate the format and report invalid values / missing args with a clean message instead of a raw stack trace (ArgError).

Tests

Added src/__tests__/args.test.ts covering the regression and every invocation form (default, --format=value, --format value, flag-first, missing args, invalid format).

Verification

no flag (was broken)  → OK
--format=json         → OK
--format markdown     → OK
flag first            → OK
invalid format        → "Invalid format: \"xml\". Supported formats: text, json, markdown." (exit 1, no stack)
missing args          → "Usage: sbom-diff <old.json> <new.json> ..." (exit 1)

npm run lint, npm run typecheck, npm test (26 passed), and npm run build all pass.

https://claude.ai/code/session_01LuhAMY6e7HPmHMGWGeCiVh

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