chore(tracker): sync Step 2.5 → ✅ and log PRs #85–#88

[officialCodeWork]

Summary

• Mark Phase 2 Step 2.5 (Hybrid RRF fusion) as ✅; record PR #86.
• Append history rows for #85 (Step 2.4 sync), #86, #87 (mypy duplicate-tests-module fix), #88 (mypy no-any-return fix in HybridRetriever policy filter).
• Refresh Last updated and Next action lines; Next action remains Step 2.6 (Query understanding), now with no blocking predecessor.

Phase 2 milestone counts (5 done / 6 remaining) were already pre-bumped in PR #83 and remain accurate after this sync.

Documentation

TRACKER.md only — no source or docs/ changes.

Test plan

• No code changes; tracker-only PR.
• Reviewer confirms PR numbers + titles match gh pr list.

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