feat(checks): add name-whitespace rule and fix model-unknown SARIF catalog gap

[protosphinx]

Why

Two small gaps in skillcheck's rule coverage:

1. A skill whose name: contains spaces or tabs cannot match any typical
   filename and creates ambiguous lookups at runtime. There was no rule
   catching this. Authors who type name: my cool skill get no signal
   from the linter today.

2. The SARIF RULES catalog was missing model-unknown. When that
   diagnostic appeared in output, the SARIF serializer fell back to a
   synthetic rule entry (id used as both name and short description),
   which produces lower-quality output in GitHub Code Scanning.

What

• src/checks.ts: add checkNameWhitespace, called from runChecks
  after checkNameDrift. Rule id: name-whitespace, severity: warn.
  Fires when /\s/.test(v.name) is true (spaces, tabs, newlines).
• src/sarif.ts: add name-whitespace and model-unknown entries to
  the RULES catalog with proper camelCase names and descriptions.
• test/checks.test.ts: 4 new test cases for name-whitespace.
• test/sarif.test.ts: 3 new test cases; also extend the existing
  full-catalog assertion to cover both new rules.

Tests

• warns when skill name contains spaces
• does not warn name-whitespace for a clean hyphenated name
• name-whitespace message includes the offending name
• warns when skill name contains a leading space
• model-unknown appears in the catalog with a proper camelCase name
• name-whitespace appears in the catalog with a proper camelCase name
• ruleIndex for name-whitespace points to the registered entry

Self-merge gate

• all CI checks pass
• LOC delta < 250 (added + removed)
• no public-API surface change
• no runtime-dependency additions
• no workflow file changes
• tests added or extended

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