fix(#484): drop noisy "parse failed" note on JSON/YAML fragments

LLMs routinely emit JSON/YAML *fragments* in fenced blocks — a bare
`"key": "value"` line, snippets with `...`, trailing commas — which
legitimately fail JSON.parse. initTreeViews() stamped an unstyled
`<div class="tree-parse-note">parse failed</div>` below such blocks,
producing bare white text under an otherwise-clean code box.

The note was incidental, not designed: it was bolted onto the YAML
lazy-load commit (29a31a6e), has no CSS, no behavior test, and originally
even fired on *valid* YAML before the CDN script finished loading (later
fixed). The block still renders as syntax-highlighted raw, so the note
added only noise.

Remove the note insertion; fall through silently to raw view. The per-block
Raw/Tree toggle, YAML lazy-load, and the #484 default-view config are all
unchanged. The `parse_failed_note` i18n key is intentionally retained (kept
green by test_chinese_locale.py) to avoid touching all 13 locales.

Verification: ./scripts/test.sh tests/test_issue484_json_tree_viewer.py
tests/test_chinese_locale.py — 29 passed.

static/ui.js

@@ -13636,15 +13636,12 @@ function initTreeViews(container){
     // Mark as initialised only after we've committed to a render decision
     wrap.setAttribute('data-tree-init','1');
     if(!parsed || typeof parsed!=='object'){
-      if(parseFailed){
-        const hint=wrap.querySelector('.tree-raw-view');
-        if(hint&&!hint.querySelector('.tree-parse-note')){
-          const note=document.createElement('div');
-          note.className='tree-parse-note';
-          note.textContent=t('parse_failed_note')||'parse failed';
-          hint.parentNode.insertBefore(note,hint.nextSibling);
-        }
-      }
+      // No tree view for non-object values or unparseable content. LLMs often
+      // emit JSON fragments (a bare "key": "val" line, snippets with ..., etc.)
+      // that legitimately fail JSON.parse; surfacing a "parse failed" note for
+      // those was pure noise. The block still renders as syntax-highlighted raw,
+      // so just fall through silently. (parseFailed is retained for clarity.)
+      void parseFailed;
       return; // leave as raw view
     }
     const lineCount=rawText.split('\n').length;