Add severity(forCrap:threshold:) band classifier

[JordanCoin]

🤖 crap4swift reviewed its own PR

This PR adds severity(forCrap:threshold:). Scoped to just this diff, crap4swift flagged it:

CRAP	CC	Coverage	Function
42 ⚠️	6	0%	severity(forCrap:threshold:) — CrapCore/Severity.swift:5

Verdict: approve-with-tests. Six branches, zero coverage → CRAP 42 (> threshold 30). The logic isn't dangerous, but it's untested branching. Add one test hitting each band (trivial / low / watch / high / severe / critical) and CRAP drops from 42 to 6.

Risk map — crap4swift --spm . --changed main --format review

{
  "base" : "main",
  "functions" : [
    {
      "complexity" : 6,
      "coverage" : 0,
      "crap" : 42,
      "endLine" : 12,
      "file" : "/Users/jordan/Code/crap4swift/Sources/CrapCore/Severity.swift",
      "function" : "severity(…)",
      "lint" : [

      ],
      "overThreshold" : true,
      "startLine" : 5
    }
  ],
  "summary" : {
    "count" : 1,
    "overThreshold" : 1,
    "worst" : "severity(…)"
  },
  "threshold" : 30
}

---

This review was generated by the tool in this repo, running against its own diff on a fresh swift test coverage run. That's the pitch: hand your AI reviewer a measured risk map, not a blind diff.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[github-actions]

crap4swift — changed-function risk

{
  "base" : "81babb68f8375c96c7cdc87dd0f10ac7fffa67a8",
  "functions" : [
    {
      "complexity" : 6,
      "coverage" : 1,
      "crap" : 6,
      "endLine" : 12,
      "file" : "/__w/crap4swift/crap4swift/Sources/CrapCore/Severity.swift",
      "function" : "severity(…)",
      "lint" : [

      ],
      "overThreshold" : false,
      "startLine" : 5
    }
  ],
  "summary" : {
    "count" : 1,
    "overThreshold" : 0,
    "worst" : "severity(…)"
  },
  "threshold" : 30
}

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[JordanCoin]

Closing — a green demo of the PR-review pipeline. severity() isn't used by the tool, so there's nothing to merge into main. The passing check + review comment remain as an example.