feat(cli): implement compare as real side-by-side renderer

[abhinav-1504]

What

Implements optiqor compare <a> <b> as a proper side-by-side renderer
instead of a diff alias.

Why

Fixes #14

How

• internal/analyze/compare.go — ComparePaths() runs analysis on
  both inputs, partitions findings into only-in-A, only-in-B, in-both
  (matched by workload+detectorID), computes cost totals, and declares
  a winner (lower cost wins; tie-break by fewer HIGH findings)
• internal/analyze/compare_render.go — WriteText() renders the
  side-by-side table; WriteJSON() emits machine-readable output with
  accuracy_disclosure; both honour the ±40% mandatory disclosure
• internal/analyze/compare_test.go — 8 unit tests covering
  partitioning, winner logic, tie detection, text/JSON renderers, and
  error paths
• cmd/optiqor/main.go — newCompareCmd() wired to ComparePaths
  instead of aliasing diff; diff unchanged

Testing

• go test ./internal/analyze/... -v — all PASS
• go build ./... — clean
• Tested locally:
  • optiqor compare a.yaml b.yaml → side-by-side table with winner
  • optiqor compare a.yaml b.yaml --json → valid JSON with accuracy_disclosure
  • optiqor compare --help → correct usage shown
  • optiqor diff still works unchanged

Checklist

• PR title follows Conventional Commits
• All commits are DCO-signed
• diff command unchanged — separate audience
• No LLM calls or telemetry introduced
• No proprietary backend imports

[github-actions]

First PR — welcome aboard!

A few things to expect:

1. CI: every PR runs build + race tests + lint on Ubuntu and macOS. If something fails, the log will tell you exactly which gate.
2. DCO: every commit needs Signed-off-by:. git commit -s adds it automatically.
3. Conventional Commits: PR titles like feat(analyze): new rule or fix(cli): handle X. We squash-merge by default.
4. Review: a maintainer will review within 72 hours. Suggestions are conversations, not orders — push back if something doesn't fit your context.

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