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/testlib.sx

@@ -0,0 +1,29 @@
+;; search test helpers — convert forced haskell values to plain SX and run
+;; programs built on top of search/src. Reuses hk-test / counters from
+;; lib/haskell/testlib.sx (preloaded by the conformance config).
+
+;; Recursively turn a forced HK value into plain SX:
+;;   cons-list  -> SX list,  Tuple -> SX list,  leaves unchanged.
+(define
+  search-hk->sx
+  (fn
+    (v)
+    (cond
+      ((and (list? v) (not (empty? v)) (= (first v) "[]")) (list))
+      ((and (list? v) (not (empty? v)) (= (first v) ":"))
+        (cons
+          (search-hk->sx (nth v 1))
+          (search-hk->sx (nth v 2))))
+      ((and (list? v) (not (empty? v)) (= (first v) "Tuple"))
+        (map search-hk->sx (rest v)))
+      (:else v))))
+
+;; Evaluate `extra` (extra top-level Haskell bindings) on top of search/src
+;; and return binding `name` as plain SX.
+(define
+  search-eval
+  (fn
+    (extra name)
+    (search-hk->sx
+      (hk-deep-force
+        (get (hk-eval-program (hk-core (str search/src extra))) name)))))