v0.0.6 — fix --judge flag, hang, and CI

Patch release: the --judge flag now works, the CLI no longer hangs after
checking, and the GitHub Actions CI is fixed. Also relicensed to MIT with a
reworked README and new contributor docs.

Fixed

• --judge now selects the proxy judge. It was parsed but ignored — every check
  ran against the AZEnv judge regardless of the flag, so the documented
  proxyjudge.us default never applied. An unknown judge name is now rejected
  with a non-zero exit (listing the valid names) and no proxies are checked.
• The CLI no longer hangs after processing all proxies. Action never closed its
  worker channel, so the worker goroutines never returned and the program blocked
  forever; the channel is now closed once the feed is exhausted.
• Rewrote the GitHub Actions workflows: pinned current Go versions, fixed the
  empty go-version in the lint job, and dropped the dead OS matrix.

Added

• ResolveJudge helper that looks a judge up in the Judges registry, and a
  NewApp constructor shared by the binary and the tests.
• CONTRIBUTING.md describing setup, the test/lint workflow, code style, and the
  commit/PR/release process.
• CHANGELOG.md, with reconstructed notes for the previously empty
  v0.0.1–v0.0.5 releases.

Changed

• Relicensed from the Apache License 2.0 to the MIT License, matching the other
  memclutter projects.
• Reworked README.md: description, status badges, install/usage, the
  tab-separated output format, a library-usage example, and a "how it works"
  explanation of judges and protocol probing.

Full changelog: v0.0.5...v0.0.6