search: Help text still mentions deduplication after collapse was removed

[tony]

Problem

`agentgrep search --help` says:

Smart search with relevance ranking, deduplication, and session grouping.

But pairwise near-duplicate collapsing was removed from the pipeline (it was O(n²) and hung on real data). Engine-level exact dedup still works via hash-based `record_dedupe_key`, but the "deduplication" in the help text implies the near-duplicate collapsing that no longer exists.

Fix

Update `SEARCH_DESCRIPTION` in `src/agentgrep/init.py` to remove or clarify the deduplication claim.