mk: matche keyword pattern fix + classic puzzles

matche-pattern->expr now treats keyword patterns as literals that emit
themselves bare, rather than wrapping in (quote ...). SX keywords
self-evaluate to their string name; quoting them flips them to a
keyword type that does not unify with the bare-keyword usage at the
target site. This was visible only as a test failure on the diffo
clauses below — tightened the pattern rules.

tests/classics.sx exercises three end-to-end miniKanren programs:
  - 3-friend / 3-pet permutation puzzle
  - grandparent inference over a fact list (membero + fresh)
  - symbolic differentiation dispatched by matche on
    :x / (:+ a b) / (:* a b)

228/228 cumulative.

plans/minikanren-on-sx.md

@@ -166,6 +166,13 @@ _(none yet)_
 
 _Newest first._
 
+- **2026-05-08** — **Classic puzzles + matche keyword fix**: matche now emits
+  keywords bare in the pattern->expr conversion so they self-evaluate to their
+  string name and unify with the same-keyword target value (instead of becoming
+  a quoted-keyword type). New `tests/classics.sx`: pet permutation puzzle,
+  parent/grandparent inference over a fact list, symbolic differentiation
+  driven by matche dispatch on `:x` / `(:+ a b)` / `(:* a b)` patterns.
+  6 new tests, 228/228 cumulative.
 - **2026-05-08** — **Phase 5 piece D — matche, Phase 5 done**: pattern matching
   macro (`lib/minikanren/matche.sx`) — symbols become fresh vars, atoms become
   literals, lists recurse positionally, repeated names unify. 14 new tests