compiler phase 1: var-indirection for redefinable compiled globals

Compiled global references now deref through the Jolt var cell instead of an
early-bound Janet symbol, so redefining a def/defn is visible to already-compiled
callers (Janet early-binds plain symbols). A global ref analyzes to :op :var
(resolving/creating the cell); a def sets that same cell's root. Because Janet
copies table constants but references functions, we embed memoized getter/setter
closures over the cell rather than the cell itself. This also subsumes the old
named-fn recursion rewrite and the separate ns-intern.

ns-intern now stores the namespace *name* (string) in a var, not the ns table, so
var cells aren't cyclic (required for embedding).

fib(30) compiled ~0.5s (the late-binding cost vs phase 2's direct-linked 0.08s;
direct-linking for hot calls is a later optimization). Suite green; cross-form,
recursion, and context isolation preserved; redefinition now works.

test/integration/compile-mode-test.janet

@@ -100,10 +100,19 @@
   (assert (= 2 (ct-eval ctx "(#{1 2 3} 2)")) "set as fn")
   (assert (= true (ct-eval ctx "(= [1 2] [1 2])")) "= is value equality, not core-= bypass"))
 
-# Context isolation: a def in one compiled context is invisible in another.
+# Context isolation: a def in one compiled context is invisible in another. With
+# var-indirection each context has its own var cells, so b's `secret` is a
+# distinct, unbound var (nil) rather than a's 7.
 (let [a (init {:compile? true}) b (init {:compile? true})]
   (eval-string a "(def secret 7)")
   (assert (= 7 (ct-eval a "secret")) "def visible in its own ctx")
-  (assert (not ((protect (ct-eval b "secret")) 0)) "def isolated to its ctx"))
+  (assert (nil? (ct-eval b "secret")) "def isolated to its ctx"))
+
+# Redefinition is visible to already-compiled callers (var-indirection).
+(let [c (init {:compile? true})]
+  (eval-string c "(defn g [] 1)")
+  (eval-string c "(defn calls-g [] (g))")
+  (eval-string c "(defn g [] 2)")
+  (assert (= 2 (ct-eval c "(calls-g)")) "compiled caller sees redefined global"))
 
 (print "\nAll Phase 6 tests passed!")