core: Stage 3 turn 2a — close the implicit Janet root-env leak

resolve-sym's last resort silently resolved any unknown Clojure symbol
against Janet's root environment — leaking Janet builtins with JANET
semantics into Clojure code: (type 1) was Janet's :number, (gensym) returned
Janet symbols (the long-documented (symbol (str (gensym))) macro landmine
existed BECAUSE of this), compare/slurp/int?/any? likewise. The explicit
janet/ prefix is the deliberate interop channel; the implicit fallback is
gone — an unresolved symbol is an error.

What the leak was masking, now proper interned vars:
- gensym: jolt's own (already existed, never interned) — returns real jolt
  symbols; the macro landmine is dead
- compare: full Clojure total order (nil-first, numbers, strings, keywords,
  symbols by ns/name, booleans, chars, uuid/inst, vectors by length then
  elementwise; cross-type throws)
- type: :type metadata override, deftype/record tag as symbol, else a
  taxonomy keyword (host-classified)
- int?: core-integer? — which had a latent bug the leak hid: (integer?
  ##Inf) was true (floor of inf is inf); NaN/infinities now excluded
- any?: constantly true (Clojure 1.9; SCI's namespaces.cljc needs it)
- jolt.interop/janet-type now uses the explicit (janet/type x) channel
- evaluator-test uses init (a bare make-ctx resolved EVERYTHING via the leak)

Suite 4470 -> 4532+ pass / 86-87 clean (proper compare unlocks the sort
files); baselines raised. Conformance 326x3 (+5 rows), +22 predicate spec
rows, stdlib battery green, all specs+unit. Coverage dashboard now counts
previously-leak-resolvable names honestly (missing-portable 19 -> 27).

test/integration/conformance-test.janet

@@ -200,6 +200,13 @@
    ["inst offset normalized" "true" "(= #inst \"2020-01-01T01:00:00+01:00\" #inst \"2020-01-01T00:00:00Z\")"]
    ["sq literal collapse" "true" "(= \"meow\" ```\"meow\")"]
    ["sq number collapse"  "42"   "``42"]
+
+   ### ---- stage 3: proper vars replace the Janet root-env leak ----
+   ["compare total order" "[-1 0 1]" "[(compare nil 1) (compare :a :a) (compare \"b\" \"a\")]"]
+   ["compare vectors"     "-1"    "(compare [1 2] [1 3])"]
+   ["gensym jolt symbol"  "true"  "(symbol? (gensym))"]
+   ["any? anything"       "true"  "(and (any? nil) (any? 1) (any? :k))"]
+   ["int? excludes Inf"   "false" "(int? ##Inf)"]
    ["macroexpand-1 when" "2"     "(count (rest (macroexpand-1 (quote (when true 1)))))"]
 
    ### ---- HIGH: aliased namespace calls ----