core: java.time + java.io shims — Selmer renders end to end (jolt-ea7)

Selmer now loads and renders templates on jolt: variables, filters
(upper, date with JVM patterns), if/for tags, nested lookups, HTML
escaping, and render-file with its last-modified template cache.

New src/jolt/javatime.janet provides the java.time surface Selmer's
date filters use (DateTimeFormatter/Instant/ZoneId/LocalDateTime/
FormatStyle/Locale, epoch-ms backed, host-local timezone) plus the
java.io/java.lang/java.net shims its template reader needs
(StringReader, StringBuilder, URL, File/separator, Class/forName).
Everything registers through three new evaluator registries
(class-statics, tagged-methods, class-ctors), so the module is data
plus an install call.

Fixes shaken out along the way, each load-bearing for Selmer and
correct on their own:
- :refer :all silently referred nothing (it iterated the :all keyword)
- ns :import ignored vector specs and didn't share deftype ctor vars
- dot calls on deftype/reify instances never consulted the protocol
  registry, so (.render-node node ctx) failed where (render-node ...)
  worked
- instance? rejected expression type args like (Class/forName "[C")
- char-array didn't accept a string
- io/resource now searches the loader's source roots (the classpath
  analog); io/reader handles char arrays, URLs, readers, and returns
  an in-memory reader with :read-line-fn for file paths
- String .split (regex, JVM trailing-empty semantics), file-path
  methods (.toURI/.toURL/.getPath/.lastModified/.exists)
- System/getProperty (os.name & co), the janet/* bridge now works
  inside env-less fibers, and qualified class names that syntax-quote
  mangles (selmer.util/StringBuilder) fall back to the ctor registry

Spec rows cover the shim surface; test/integration/selmer-test.janet
runs the real Selmer from ~/src/selmer (skips cleanly when absent).

test/integration/selmer-test.janet

@@ -0,0 +1,61 @@
+# Selmer acceptance (jolt-ea7): load the real Selmer template engine from
+# ~/src/selmer and render through its full pipeline — the java.time shims
+# (DateTimeFormatter/Instant/ZoneId/LocalDateTime), the java.io shims
+# (StringReader/StringBuilder + char-array readers), vector :import sharing
+# deftype ctors, and :refer :all. SKIPS cleanly if the checkout is absent
+# (CI has no ~/src/selmer); the shim surface itself is covered by
+# test/spec/host-interop-spec.janet either way.
+
+(import ../../src/jolt/api :as api)
+(use ../../src/jolt/reader)
+
+(def selmer-src (string (os/getenv "HOME") "/src/selmer/src"))
+(def selmer-res (string (os/getenv "HOME") "/src/selmer/resources"))
+
+(if (nil? (os/stat (string selmer-src "/selmer/parser.clj")))
+  (print "selmer-test: ~/src/selmer not present, skipping")
+  (do
+    (reader-features-set! ["jolt" "clj" "default"])
+    (def ctx (api/init {:paths [selmer-src selmer-res]}))
+
+    (print "loading selmer.parser...")
+    (api/eval-string ctx "(require (quote [selmer.parser :as sp]))")
+    (print "  ok")
+
+    (defn render [tpl ctx-map-src]
+      (api/eval-string ctx (string "(sp/render " (describe tpl) " " ctx-map-src ")")))
+
+    (print "variable + filter...")
+    (assert (= "Hello WORLD!" (render "Hello {{name|upper}}!" "{:name \"world\"}")))
+    (print "  ok")
+
+    (print "date filter (java.time path)...")
+    (def d (render "{{d|date:yyyy-MM-dd}}" "{:d #inst \"2020-03-05T10:00:00Z\"}"))
+    (assert (peg/match '(* :d :d :d :d "-" :d :d "-" :d :d -1) d)
+            (string "date filter renders a yyyy-MM-dd date, got: " d))
+    (print "  ok")
+
+    (print "if / for tags...")
+    (assert (= "YES" (render "{% if ok %}YES{% else %}NO{% endif %}" "{:ok true}")))
+    (assert (= "NO" (render "{% if ok %}YES{% else %}NO{% endif %}" "{:ok false}")))
+    (assert (= "1,2,3," (render "{% for x in xs %}{{x}},{% endfor %}" "{:xs [1 2 3]}")))
+    (print "  ok")
+
+    (print "nested lookup + escaping...")
+    (assert (= "7" (render "{{m.a.b}}" "{:m {:a {:b 7}}}")))
+    (assert (= "&lt;b&gt;&amp;" (render "{{x}}" "{:x \"<b>&\"}")))
+    (print "  ok")
+
+    (print "file templates (render-file + cache)...")
+    (def tpl-dir (string (or (os/getenv "TMPDIR") "/tmp") "/jolt-selmer-test"))
+    (os/mkdir tpl-dir)
+    (spit (string tpl-dir "/t.html") "File says {{x|upper}}")
+    (api/eval-string ctx (string "(selmer.util/set-custom-resource-path! " (describe (string tpl-dir "/")) ")"))
+    (assert (= "File says HI"
+               (api/eval-string ctx "(sp/render-file \"t.html\" {:x \"hi\"})")))
+    # second render goes through the template cache (last-modified check)
+    (assert (= "File says AGAIN"
+               (api/eval-string ctx "(sp/render-file \"t.html\" {:x \"again\"})")))
+    (print "  ok")
+
+    (print "selmer-test: all passed")))