reflective: extract quoting.sx — Kernel + Scheme share quasiquote walker

lib/guest/reflective/quoting.sx — quasiquote walker with adapter cfg.
Three forms:
- refl-quasi-walk-with CFG FORM ENV       (top-level)
- refl-quasi-walk-list-with CFG FORMS ENV (list walker, splice-aware)
- refl-quasi-list-concat XS YS            (pure-SX helper)

Adapter cfg keys:
- :unquote-name           — string keyword ("$unquote" or "unquote")
- :unquote-splicing-name  — string keyword
- :eval                   — fn (form env) → value

The shared algorithm is identical in Kernel and Scheme; the only
divergences are the keyword names (`$unquote` vs `unquote`) and
which host evaluator runs at unquote points (`kernel-eval` vs
`scheme-eval`). Both surface through the cfg.

Migrations:
- lib/kernel/runtime.sx: knl-quasi-walk reduces to a 3-line wrapper
  that builds knl-quasi-cfg and delegates. Removed knl-quasi-walk-
  list + knl-list-concat (~40 LoC) — now provided by the kit.
- lib/scheme/eval.sx: scm-quasi-walk reduces to a 3-line wrapper
  around scm-quasi-cfg. Removed scm-quasi-walk-list + scm-list-
  concat. scm-collect-exports (module impl) was a hidden consumer
  of scm-list-concat — rewired to refl-quasi-list-concat.

lib/scheme/test.sh — loads lib/guest/reflective/quoting.sx before
lib/scheme/parser.sx so the kit is available when eval.sx loads.

Both consumers' tests green:
- Kernel: 322 tests across 7 suites
- Scheme: 296 tests across 9 suites

**Second reflective-kit extraction landed.** The kit-extraction
playbook from env.sx and class-chain.sx — adapter-cfg pattern from
lib/guest/match.sx, same algorithm bridges different keyword names —
works again on a third structurally different problem (quasiquote
walking). The cumulative extraction story: env.sx → class-chain.sx
→ quoting.sx, three independent kits, all using the same pattern.

`evaluator.sx` (the other deferred candidate the Scheme port
unlocked) is NOT extracted — the genuinely shared content is too
thin (one helper for closure-capturing interaction-environment).
The eval-protocol is more about API surface than algorithm.
Documented as a non-extraction.

lib/guest/reflective/quoting.sx

@@ -0,0 +1,77 @@
+;; lib/guest/reflective/quoting.sx — quasiquote walker.
+;;
+;; Extracted from Kernel's `knl-quasi-walk` and Scheme's `scm-quasi-walk`,
+;; which differ only in:
+;;   - the unquote keyword name (Kernel: "$unquote" / "$unquote-splicing";
+;;     Scheme: "unquote" / "unquote-splicing")
+;;   - the host evaluator function (`kernel-eval` vs `scheme-eval`)
+;;
+;; Algorithm is identical. Adapter cfg parameterises the two
+;; language-specific knobs.
+;;
+;; Adapter cfg keys
+;; ----------------
+;;   :unquote-name           — string, name of the unquote keyword
+;;   :unquote-splicing-name  — string, name of the splice keyword
+;;   :eval                   — fn (form env) → value
+;;
+;; Public API
+;;   (refl-quasi-walk-with CFG FORM ENV)
+;;     Top-level walker. Returns FORM with unquotes evaluated in ENV.
+;;
+;;   (refl-quasi-walk-list-with CFG FORMS ENV)
+;;     Walks a list of forms, splicing unquote-splicing results inline.
+;;
+;;   (refl-quasi-list-concat XS YS)
+;;     Pure-SX list append (no host append/append! needed).
+
+(define
+  refl-quasi-list-concat
+  (fn
+    (xs ys)
+    (cond
+      ((or (nil? xs) (= (length xs) 0)) ys)
+      (:else (cons (first xs) (refl-quasi-list-concat (rest xs) ys))))))
+
+(define
+  refl-quasi-walk-with
+  (fn
+    (cfg form env)
+    (cond
+      ((not (list? form)) form)
+      ((= (length form) 0) form)
+      ((and (string? (first form)) (= (first form) (get cfg :unquote-name)))
+        (cond
+          ((not (= (length form) 2))
+            (error
+              (str (get cfg :unquote-name) ": expects exactly 1 argument")))
+          (:else ((get cfg :eval) (nth form 1) env))))
+      (:else (refl-quasi-walk-list-with cfg form env)))))
+
+(define
+  refl-quasi-walk-list-with
+  (fn
+    (cfg forms env)
+    (cond
+      ((or (nil? forms) (= (length forms) 0)) (list))
+      (:else
+        (let
+          ((head (first forms)))
+          (cond
+            ((and (list? head) (= (length head) 2) (string? (first head)) (= (first head) (get cfg :unquote-splicing-name)))
+              (let
+                ((spliced ((get cfg :eval) (nth head 1) env)))
+                (cond
+                  ((not (list? spliced))
+                    (error
+                      (str
+                        (get cfg :unquote-splicing-name)
+                        ": value must be a list")))
+                  (:else
+                    (refl-quasi-list-concat
+                      spliced
+                      (refl-quasi-walk-list-with cfg (rest forms) env))))))
+            (:else
+              (cons
+                (refl-quasi-walk-with cfg head env)
+                (refl-quasi-walk-list-with cfg (rest forms) env)))))))))