feat(repl): usability batch - errors, WORDS, .S, BYE, DUMP, history

Core:
- Uncaught THROW prints its standard message ("Stack underflow
  (throw -4)"; unknown codes as "Catch = <n>") instead of the
  "forth-throw" sentinel. ABORT" text is carried as a structured
  payload and shown only when the -2 throw goes uncaught -- CATCH
  stays silent and the payload cannot go stale. ABORT throws -1
  through the same path.
- WORDS: optional same-line substring filter (WORDS FDEPTH), skips
  internal words (new INTERNAL header flag, set at create for
  underscore-prefixed names), wraps at 78 columns, prints a count.
  ORDER names wids (FORTH / wid#N) instead of Rust debug output.
- .S honors BASE. New: F.S (float stack), DUMP (hex+ASCII,
  bounds-checked, 4K cap), ? (fetch-and-print, boot.fth). BYE is a
  real word now: sets a VM flag the driver honors (exits REPL,
  stops rest of line/file).

CLI:
- Persistent history (~/.local/state/wafer/history, 0600 perms,
  $WAFER_HISTORY override), Tab completion over the live dictionary
  (snapshot refreshed after each line), Up/Down do prefix history
  search, Ctrl-C clears the line instead of exiting.

Web:
- History survives reloads (localStorage, cap 200, dedup, init-code
  runs excluded), User Words palette populated via new words()
  export, stack bar annotates non-decimal BASE, base() reads the
  real BASE sysvar instead of returning a hardcoded 10.

crates/core/boot.fth

@@ -243,6 +243,9 @@
 \ U. ( u -- )  print unsigned number and space
 : U.  0 <# #S #> TYPE SPACE ;
 
+\ ? ( a-addr -- )  fetch and print
+: ?  @ . ;
+
 \ .R ( n width -- )  print right-justified signed number
 : .R  >R DUP ABS 0 <# #S ROT SIGN #> R> OVER - SPACES TYPE ;