fix(kb): RTL-correct pane order + new-result button + 30-min auto-clear

Three issues from the v0.2.0 user test:

1. Sides flipped relative to expectation
   In our Hebrew/RTL CRM the user reads primary content (the answer or
   the hit list) on the visual right and the supporting reference
   (the PDF) on the visual left — that's how Hebrew layouts stage
   "main + sidebar". v0.1.10's _buildSplitShell forced direction:ltr on
   the splitter container (correct, for mouseX math) but laid the
   children in the order [primary, handle, reference], which under LTR
   put primary on the LEFT and PDF on the RIGHT. Fixed by renaming the
   helper params to {primaryHtml, referenceHtml} and ordering the
   children as [reference, handle, primary] — visual LEFT is now the
   PDF, visual RIGHT is the answer/list. Default split moved from 42%
   to 58% so the reference pane (now on the left) keeps the same
   absolute width the PDF column had under v0.1.9's bootstrap rows.

2. No way to start a new query
   afterRender replays _lastSearch / _lastAsk on every remount, which
   means the prior result hangs around forever. Added a "חיפוש חדש" /
   "שאלה חדשה" button next to the submit button. clearResults() cancels
   any in-flight request (closes the EventSource for ask, drops
   _activeSearch reference for search), removes the cached entry from
   sessionStorage, empties the results pane, and refocuses the input.

3. Stale results from another session
   Cached results now auto-expire after 30 minutes — _loadJson checks
   completedAt against STALE_AFTER_MS and silently drops anything
   older. So coming back tomorrow the KB tab opens clean instead of
   showing yesterday's answer to whatever you asked then.

Refs Task Master #4, #6

files/client/custom/modules/knowledge-base/res/templates/kb/index.tpl

@@ -28,6 +28,8 @@
                 <option value="circular">חוזרים</option>
             </select>
             <button type="button" class="btn btn-primary" data-action="submit">חפש</button>
+            <button type="button" class="btn btn-default" data-action="clearResults"
+                    title="התחל חיפוש חדש (מנקה את התוצאות הקודמות)">חיפוש חדש</button>
         </div>
         <div class="small text-muted" style="margin-top:6px;">
             חיפוש Hybrid: וקטורי + מילולי + rerank. מחזיר עד 8 קטעים רלוונטיים.
@@ -42,6 +44,8 @@
                    placeholder="שאלה בשפה חופשית…"
                    style="flex:1 1 320px;min-width:280px;" />
             <button type="button" class="btn btn-primary" data-action="submit">שאל את שירה</button>
+            <button type="button" class="btn btn-default" data-action="clearResults"
+                    title="התחל שאלה חדשה (מנקה את התשובה הקודמת)">שאלה חדשה</button>
         </div>
         <div class="small text-muted" style="margin-top:6px;">
             שירה תחפש בבסיס הידע ותחזיר תשובה מסוכמת עם ציטוטים.