fix(runtime): Random.* in any program; value_* called directly brings the value tree

The seeded random numbers lived in the ECS runtime, so a tool or a
program of test blocks got "unknown function rng_range". They are
runtime/native/rng.ludic now, spliced on Random.* or a bare rng_*/seed
call nobody defines, and imported by core.ludic for a game. A bare
value_*/json_* call nothing in the program defines splices the value
tree the way Value.* does. Reseed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/library/random_plain.ludic

@@ -0,0 +1,19 @@
+# random_plain.ludic — Random.* in a program with no properties or handlers: the seeded random
+# numbers are spliced on their own, and a helper may call rng_range directly. The same seed gives
+# the same draws.
+#
+# Running it prints:  1 1 1
+program RandomPlain {
+  function roll() -> int {
+    return rng_range(1, 6)
+  }
+  entry {
+    Random.seed(7)
+    let a = Random.range(1, 6)
+    let b = roll()
+    Random.seed(7)
+    let c = Random.range(1, 6)
+    let d = roll()
+    print(`{a == c} {b == d} {a >= 1 and a <= 6}`)
+  }
+}