Add unpriced filter to models report

[kocaemre]

Why

Related to #969.

The TUI warning for unpriced models points users at codeburn model-alias, but the detailed model list is still hard to reach/copy from the dashboard. codeburn models is already the plain-stdout escape hatch, so this adds a focused filter for the affected rows.

What

• Adds codeburn models --unpriced.
• Keeps zero-cost unpriced rows visible by defaulting that mode's min-cost threshold to 0.
• Reuses the existing findUnpricedModels logic so local/free/aliased/overridden models are treated the same as the dashboard warning.
• Covers the CLI path with a fixture containing one priced model and one unpriced model.

Validation

• npx vitest run tests/models-report.test.ts
• npm run build:cli
• Manual fixture run:
  • node dist/cli.js models --unpriced --from 2026-05-09 --to 2026-05-09 --provider claude --format json

Note

I also tried npm test -- tests/models-report.test.ts, but the script ignores the positional file argument and ran the broad suite. That broad run failed in unrelated cache/history CLI tests due the local environment picking up existing usage data; the targeted suite above passes.