JOLT_TRACE: honor the env at runtime in a built joltc

The JOLT_TRACE opt-in was a top-level form in compile-eval.ss, so in a
self-contained joltc it ran at heap-build time — where JOLT_TRACE is always
unset — and never at runtime. `JOLT_TRACE=1 joltc -M:run` therefore produced no
trace from the distributed binary (it worked only under the source-loaded dev
launcher). REPL/nREPL tracing was unaffected (those enable at runtime).

Make it a jolt-trace-init-from-env! fn called from the runtime entrypoints — the
cli.ss dispatch and the built-joltc launcher — before any app namespace compiles,
so the app's own code is traced. While here, drop a redundant trace print in the
joltc launcher (jolt-report-throwable already emits it) that double-printed the
block once tracing actually produced one.

joltc-selfbuild-smoke asserts JOLT_TRACE=1 through the built binary yields exactly
one tail-frame trace.

host/chez/cli.ss

@@ -66,6 +66,9 @@
       (when bt (display "  trace:\n" port) (display bt port)))
     (exit 1)))
 
+;; JOLT_TRACE opt-in, at runtime (before any app ns compiles) so the app is traced.
+(jolt-trace-init-from-env!)
+
 (guard (v (#t (jolt-report-uncaught v)))
   (cond
     ;; -e EXPR — evaluate one expression and print it (blank for nil). Wrapped in