feat(scanner): add finding deduplication to ResultAggregator

[Senthemodder]

Fixes #20

Summary

Adds result deduplication to ResultAggregator for findings targeting the same file, line range, and vulnerability category.

Changes

• Implemented deduplicateFindings() on ResultAggregator:
  • Groups findings by ${filePath}:${lineStart}:${lineEnd}:${category} (with fallback to pluginId when category is absent).
  • Prioritizes findings by severity rank: CRITICAL > HIGH > MEDIUM > LOW > GAS > INFORMATIONAL.
  • On equal severity, retains the finding with higher confidence.
• Updated summarize() to compute summary totals and severity breakdowns over deduplicated results.
• Added optional category property to FindingResult in @veridion/scanner-types and @veridion/shared.
• Authored comprehensive test suite in packages/scanner-core/src/result-aggregator.test.ts verifying duplicate retention, severity prioritization, confidence tie-breaking, distinct location handling, and summary metrics.

Verification

• pnpm --filter @veridion/scanner-core test: 21/21 passed (16 deduplication tests + 5 registry tests).
• pnpm --filter @veridion/scanner-core typecheck: 0 errors.
• pnpm --filter @veridion/scanner-core lint: 0 warnings.
• Full workspace verification: 39/39 turbo tasks passed.

[Kami-no-san]

Good Day, @Senthemodder Please fix failing CI