revert: replace fullwidth pipe ｜ with halfwidth | in DSML tool markup

PR #460 introduced fullwidth pipe characters (｜) in DSML tool call formatting
to improve parsing robustness, but models exposed to these fullwidth pipes in
system prompts exhibit significantly higher rates of tool output hallucinations.
Reverting to halfwidth pipes (|) drastically reduces tokenizer/perplexity-driven
hallucinations while retaining the existing confusable-hardening in the parser.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/js/helpers/stream-tool-sieve/parse_payload.js

@@ -1356,7 +1356,7 @@ function consumeToolMarkupPipe(raw, idx) {
   if (pos >= raw.length) {
     return { next: idx, ok: false };
   }
-  for (const variant of ['|', '｜', '│', '∣', '❘', 'ǀ', '￨']) {
+  for (const variant of ['|', '│', '∣', '❘', 'ǀ', '￨']) {
     if (raw.startsWith(variant, pos)) {
       return { next: pos + variant.length, ok: true };
     }