chore(sow)+test(downloader): rename slice label and extend /0 filter assertion

[ktsaou]

Summary

Follow-up to PR #37. Addresses 2 more small, mechanical items from the
AI code quality findings triage:

• SOW-0102: rename the first slice's result heading from
  Final local results to First-slice local results. The SOW now
  documents three slice results (First, Second, Third), so the original
  Final label was misleading for readers scanning the document.
• pkg/downloader: extend the /0 filter test in
  TestParseProcessedFeedFileSanitizesInput to also assert that
  5.6.7.0 (the CIDR base address) is omitted alongside 5.6.7.1.
  This catches regressions where the /0 base is kept while other
  addresses inside the range are dropped.

Diff size

SOW-0102: 1 line
canonical_test.go: 1 line (added "5.6.7.0" to existing assertCanonicalSetOmits call)

Validation

• go test ./pkg/downloader/... — pass
• go test -race ./pkg/downloader/... — pass

Out of scope (still)

The remaining 6 skipped findings are addressed in the PR #37 triage
table. The next-largest candidates (slice ordering, status change) are
intentionally deferred because they conflict with project conventions
or would require renumbering thousands of lines.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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_{TIP This summary will be updated as you push new changes.}