Fix: HtmlBlock sanitizer strips select/meter presentation attrs

size, low, high, and optimum were missing from PURIFY_CONFIG.ALLOWED_ATTR
even though <select> and <meter> are already in ALLOWED_TAGS, so
<select size="4"> rendered at default height and <meter low/high/optimum>
lost its threshold-based gauge colouring. All four are pure
presentation/semantic attributes with no URL/script/event-handler
surface, so no security implication.

Also regenerates the pinned pre-Task-25 output fixture: its source
(html-block-test-body.html) already exercises size/low/high/optimum, so
the byte-identity test's expected output legitimately changes to include
them; verified the regenerated fixture's only diff from the prior one is
those four attributes now surviving.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

craft/src/components/basic/__fixtures__/html-block-test-body.pre-task25-output.html

@@ -266,7 +266,7 @@ here</textarea></p>
         </p>
         <p>
           <label for="f-multi">Multi-select</label><br>
-          <select id="f-multi" multiple="">
+          <select id="f-multi" multiple="" size="4">
             <option>Red</option><option selected="">Green</option><option>Blue</option><option>Violet</option>
           </select>
         </p>
@@ -275,7 +275,7 @@ here</textarea></p>
       <fieldset>
         <legend>Output and buttons</legend>
         <p><label for="f-prog">Progress</label> <progress id="f-prog" value="0.6">60%</progress></p>
-        <p><label for="f-meter">Meter</label> <meter id="f-meter" min="0" max="100" value="72">72</meter></p>
+        <p><label for="f-meter">Meter</label> <meter id="f-meter" min="0" max="100" low="30" high="80" optimum="90" value="72">72</meter></p>
         <p><output name="result" for="f-num f-range">Computed output</output></p>
         <p>
           <button type="submit">Submit</button>