v4.7.0: Add domain reputation/blocklist data source

- New DomainReputationResult model (status: clean/listed/unknown, listed
  sources, checked-at) and a `reputation(domain:)` method on ExternalDataService,
  mirroring the existing pluggable-URL enrichment pattern (ownership history,
  DNS history, extended subdomains, pricing). With no endpoint configured
  (the default; DomainDig ships no bundled third-party reputation dependency)
  it resolves to unavailable rather than "clean".
- New .reputation FeatureCapability/DataCapability, gated Pro+ like domainPricing.
- Threaded reputation/reputationError through LookupSnapshot and HistoryEntry
  (backward-compatible decode) so results persist with history entries.
- Auto-fetched in performLookup alongside pricing; surfaced as a "Reputation"
  info row, folded into DomainInsightEngine's risk score/factors and top-level
  insights (a listed domain raises risk score and adds a factor/insight), and
  exported in text, CSV, and JSON report output.
- Reputation-driven risk changes ride the existing change-severity pipeline, so
  a listed status flip is visible to monitoring the same way any other risk
  delta is, without bespoke monitoring wiring.

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