fix(web): surface Forth messages from host-word throws

A host word signals failure by throwing across the JS boundary, and the
browser runtime reported that exception with its Debug form, so an
empty-stack RESIZE surfaced as

    call_func(134) failed: JsValue(Error: Stack underflow ...)

with the engine's JS stack trace glued on. The thrown message IS the
Forth message, so take it verbatim: 'Stack underflow', the same text the
native CLI prints. Exceptions without a message keep the call context --
those are genuine runtime faults, not Forth throws.

CATCH is unaffected: it reads the throw code from its own channel rather
than parsing messages. Verified against a fresh VM in Node (initSync +
WaferRepl): host-word underflow, compiled-guard underflow, THROW,
unknown word and ' RESIZE CATCH . all match the native CLI.

Ships as v0.2.4.

Cargo.lock

@@ -1589,7 +1589,7 @@ checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
 [[package]]
 name = "wafer"
-version = "0.2.3"
+version = "0.2.4"
 dependencies = [
  "anyhow",
  "clap",
@@ -1600,7 +1600,7 @@ dependencies = [
 
 [[package]]
 name = "wafer-core"
-version = "0.2.3"
+version = "0.2.4"
 dependencies = [
  "anyhow",
  "insta",
@@ -1615,7 +1615,7 @@ dependencies = [
 
 [[package]]
 name = "wafer-web"
-version = "0.2.3"
+version = "0.2.4"
 dependencies = [
  "anyhow",
  "js-sys",