Clean up codebase: rename stdlib layer, strip porting residue, fix tooling

Rename src/jolt -> stdlib (the runtime-loaded layer; jolt-core stays the
seed-baked layer) and update the loader / emit-image / doc paths. Drop dead
code: the spike/ experiments, the duplicate clojuredocs-export.edn (json moves
to tools/), the Janet-era jolt.http binding, and the orphaned
persistent_vector.clj whose ns/path didn't even match.

Strip porting residue from comments and docstrings across host/chez, jolt-core,
stdlib, tests, and docs: internal issue ids, "Phase N" markers, and the "vs
Janet" historical exposition, leaving present-tense descriptions and the real
JVM-Clojure semantic contrasts. Same pass over the corpus suite labels. The seed
is unchanged (docstrings/comments aren't emitted), so the self-host fixpoint and
corpus are untouched.

Port tools/spec_coverage.py off the dead janet probe to bin/joltc and regenerate
coverage.md; drop the dead :host/janet rule from certify.clj and regenerate the
conformance profile. Add docs/host-interop.md (the JVM shims and how to register
your own host class from a library) and a writing-style note in CLAUDE.md.

Stabilize the four racy concurrency corpus cases (future-cancel and agent
send/send-off): give the future a sleeping body and the agent a slow action, so
cancel reliably catches an in-flight future and deref reliably reads the
pre-update snapshot. They certify deterministically now, so drop their :flaky
allowlist entries and the orphaned legend.

stdlib/clojure/pprint.clj

@@ -0,0 +1,33 @@
+;; clojure.pprint — minimal jolt shim.
+;;
+;; The real clojure.pprint is a full pretty-printer (thousands of lines of column
+;; tracking / dispatch tables). This shim provides just the surface that portable
+;; libraries reach for when they "pretty print" a value — notably
+;; clojure.tools.logging/spy (pprint + with-pprint-dispatch + code-dispatch).
+;; pprint writes the value readably with a trailing newline (no pretty layout);
+;; the dispatch vars are recognized but not used for layout.
+(ns clojure.pprint)
+
+(def code-dispatch
+  "Recognized but not used for layout on jolt." :code-dispatch)
+(def simple-dispatch
+  "Recognized but not used for layout on jolt." :simple-dispatch)
+
+(def ^:dynamic *print-pprint-dispatch* simple-dispatch)
+
+(defn pprint
+  "Print object readably followed by a newline. Not a pretty-printer on jolt —
+  no column-aware layout. jolt routes all printing through the host output seam
+  (with-out-str captures it), and *out* is not a bindable var, so an explicit
+  writer arg is accepted for API compatibility but not honored — output goes to
+  the current output. (The old `(binding [*out* writer] ...)` never redirected
+  anything either, and made the defn fall back to the interpreter; dropping it
+  lets pprint compile cleanly, which the no-fallback Chez back end requires.)"
+  ([object] (prn object))
+  ([object _writer] (prn object)))
+
+(defmacro with-pprint-dispatch
+  "Evaluate body with the given pprint dispatch selected. On jolt the dispatch is
+  recognized but does not affect layout, so this just evaluates body."
+  [_dispatch & body]
+  `(do ~@body))