style(table): move the column picker into the table header corner

The show/hide-columns gear only makes sense in table view but sat in the
global toolbar (needing applyColsWrapVisibility to hide it elsewhere). Build
it inside the actions-column header cell in renderTable instead, with inline
handlers (recreated each render, so no dependence on once-wired listeners on
a static node). Removed #colsWrap from the toolbar + the now-obsolete
applyColsWrapVisibility and its callers; kept the menu id so
renderTableColsMenu still populates it, and a live-queried outside-click close.
Added .cols-wrap CSS (was an inline position:relative on the old node).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

index.html

@@ -286,12 +286,6 @@
                         <svg><use href="#i-table"/></svg>
                     </button>
                 </div>
-                <div class="cols-wrap" id="colsWrap" style="display:none;position:relative">
-                    <button class="icon-btn" id="colsBtn" title="Show / hide columns">
-                        <svg><use href="#i-settings"/></svg>
-                    </button>
-                    <div class="cols-menu is-hidden" id="colsMenu"></div>
-                </div>
                 <div class="filters-wrap">
                     <button class="icon-btn" id="filtersBtn" title="Filters">
                         <svg><use href="#i-list"/></svg>