errors: user-readable messages and stack traces (jolt-2o7 rounds 1+2)

Before: (+ 1 "a") printed 'could not find method :+ for 1 or :r+ for "a"'
followed by three janet frames pointing at jolt internals. After:

    Error: Cannot add 1 and "a" — + expects numbers
      at app.deep/level3

Round 1 — compiled fns carry their Clojure identity:
- The analyzer's recur target (which doubles as the compiled janet fn's
  name) is now ns/fn-name (_r$app.deep/level3--N), so janet stack traces
  name the user's fns; defn passes the self-name through to fn.
- eval-toplevel re-raises with propagate instead of protect+error — the
  failing fiber's stack was being discarded, which is why every trace began
  at eval-toplevel.
- require/maybe-require-ns route loaded namespaces through the loader's
  compile-or-interpret eval-toplevel via a ctx hook (the evaluator can't
  import the loader). Previously REQUIRED namespaces always ran interpreted:
  slower, and their fns were anonymous in traces.

Round 2 — report-error presents for users (rephrase-inspired):
- The full trace text is stashed at the innermost eval-toplevel boundary
  (janet's debug/stacktrace walks the fiber propagation chain; debug/stack
  cannot), then filtered: _r$ frames demangled to ns/fn-name, jolt-internal
  and [eval] frames dropped. JOLT_DEBUG=1 restores the raw janet trace.
- Message rewrites: janet arithmetic dispatch -> 'Cannot add X and Y — +
  expects numbers'; compiled arity -> Clojure's 'Wrong number of args (N)
  passed to: ns/fn'; nil-call gets an undefined-symbol hint (round 3 will
  fix resolution properly).

6 cli-test rows assert the exact user-visible output. Gate green, suite
4718 steady, bench within noise.

jolt-core/clojure/core/00-syntax.clj

@@ -342,7 +342,9 @@
   (let [body (if (and (seq body) (string? (first body))) (rest body) body)
         body (if (and (seq body) (map? (first body)) (not (symbol? (first body))))
                (rest body) body)]
-    `(def ~fn-name (fn ~@body))))
+    ;; pass the name through to fn: the compiled fn's janet name carries it,
+    ;; so stack traces read app.deep/level3 instead of a gensym (jolt-2o7.1)
+    `(def ~fn-name (fn ~fn-name ~@body))))
 
 ;; Jolt doesn't enforce privacy, so defn- is just defn (matching how Clojure's own
 ;; defn- delegates to defn with :private metadata).