bake the .clj stdlib into the binary

The Clojure stdlib namespaces (clojure.string/set/walk/edn/zip, jolt.http/
interop/shell/nrepl) were loaded cwd-relative, so the built binary couldn't
load them outside the repo. Now stdlib_embed slurps them all at build time into
a {ns -> source} map frozen in the image, and the loader falls back to it when a
namespace isn't found on disk. The artifact is self-contained — clojure.string
works from any directory.

Drops the one-off nREPL source embed (jolt.nrepl is covered by this now). The
baked-in stdlib is excluded from uberscript bundles since it's part of the
runtime. clojure.core is unchanged (Janet, auto-referred).

Test: embedded-stdlib-test requires from the embedded copy with FS roots cleared.

doc/building-and-deps.md

@@ -13,7 +13,11 @@ jpm build
 
 This produces two executables under `build/`:
 
-- **`jolt`** — the runtime: REPL, file/expr runner, nREPL server.
+- **`jolt`** — the runtime: REPL, file/expr runner, nREPL server. The whole `.clj`
+  standard library (`clojure.string`/`set`/`walk`/`edn`/`zip`, `jolt.http`/
+  `interop`/`shell`/`nrepl`) is baked into this binary at build time, so it loads
+  from any directory — the build artifact is self-contained. (`clojure.core` is
+  built into the runtime in Janet and auto-referred, so it's always available.)
 - **`jolt-deps`** — a separate tool that resolves a `deps.edn` (see below). It
   sits beside the runtime the way `jpm` sits beside `janet`; the runtime itself
   knows nothing about deps.edn.
@@ -37,6 +41,10 @@ come from:
   at runtime;
 - the `:paths` option to `init` when embedding Jolt as a library.
 
+If a namespace isn't found on any root, the loader falls back to the stdlib baked
+into the binary — that's how `clojure.string` and friends resolve when you run
+the binary outside the source tree.
+
 So you can point Jolt at a directory of Clojure source with no deps machinery at
 all: