search: Phase 1 tokenizer + inverted index + 18 tests

Tokenizer (lowercase, strip punctuation, positions) and a sorted assoc-list
inverted index [(Term,[(DocId,[Pos])])] with indexDoc/deleteDoc/lookupTerm/
docFreq/allTerms. Search lib is haskell-on-sx source assembled into search/src;
tests reuse hk-test counters via a search-eval helper. conformance.sh models
lib/haskell.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/search/api.sx

@@ -0,0 +1,7 @@
+;; search public API — assembles the canonical Haskell source from all layers.
+;; Tests and callers concatenate `search/src` with their own top-level bindings
+;; (e.g. "result = lookupTerm \"cat\" idx\n") and evaluate via the haskell-on-sx
+;; interpreter. Public Haskell entry points: indexDoc, lookupTerm, deleteDoc,
+;; docFreq, allTerms, tokens, positioned.
+
+(define search/src (str search/tokenize-src "\n" search/index-src))