runs filter: add J (jitter) chip group alongside N and T

app/web/static/runs-filter.js

@@ -11,6 +11,7 @@
     { prop: 'embedder',  chipsId: 'runs-flt-algo',    numeric: false },
     { prop: 'n',         chipsId: 'runs-flt-n',       numeric: true  },
     { prop: 't',         chipsId: 'runs-flt-t',       numeric: true  },
+    { prop: 'j',         chipsId: 'runs-flt-j',       numeric: true  },
   ];
 
   for (const ax of AXES) {

app/web/templates/_runs.html

@@ -11,7 +11,8 @@
           data-embedder="{{ r.embedder_short or '' }}"
           data-generator="{{ r.generator_short or '' }}"
           data-n="{{ r.params.get('num_points', '') if r.params else '' }}"
-          data-t="{{ r.params.get('num_timesteps', r.params.get('num_snapshots', '')) if r.params else '' }}">
+          data-t="{{ r.params.get('num_timesteps', r.params.get('num_snapshots', '')) if r.params else '' }}"
+          data-j="{{ r.params.get('jitter_scale', '') if r.params else '' }}">
         {% if r.emb_exists and not r.stale %}
           <input type="checkbox" class="compare-cb" data-stem="{{ r.emb_file[:-5] }}" aria-label="select run for comparison" />
         {% else %}

app/web/templates/index.html

@@ -328,6 +328,10 @@
           <span class="ctl-label">T</span>
           <div class="chips" id="runs-flt-t" aria-label="filter by T"></div>
         </div>
+        <div class="runs-filter-group" data-axis="j">
+          <span class="ctl-label">J</span>
+          <div class="chips" id="runs-flt-j" aria-label="filter by J"></div>
+        </div>
       </div>
     </div>
 
@@ -497,7 +501,7 @@
 <script type="module" src="/static/dataset-picker.js?v=11"></script>
 <script type="module" src="/static/metrics.js?v=11"></script>
 <script src="/static/compare-select.js?v=2"></script>
-<script src="/static/runs-filter.js?v=3"></script>
+<script src="/static/runs-filter.js?v=4"></script>
 <script type="module" src="/static/run-modal.js?v=3"></script>
 <script>
   // Anchor-links alone don't expand <details>; force it.