feat(toolbar): move "+" and the case gear into the case picker

The owner asked to drop the "+" (Add Case) and gear (case settings) buttons
beside the toolbar case picker. Their two actions now close the picker's own
list instead, as "New or link a case…" and "Case settings…" rows in a sticky
footer, so nothing becomes unreachable: on desktop the "+" was the only door to
Add Case (create, link, clone, manage), and the gear the only one to the
per-case Agent Teams / 1M Opus overrides.

The rows are part of the arrow-key walk (after the last case) and Enter runs
them, they also show when nothing matches the filter, and the case settings
popover still opens anchored to the case group. The picker input gets its
right-hand corners back, and the dead .btn-case-add / .btn-case-settings rules
(desktop, phone and two skin selector lists) are gone. Phones keep their own
case sheet and gear.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/web/public/index.html

@@ -722,8 +722,9 @@
             <select id="quickStartCase" class="toolbar-select case-native-select" title="Select case" aria-hidden="true" tabindex="-1">
               <option value="testcase">testcase</option>
             </select>
-            <button class="btn-case-add" onclick="app.showCreateCaseModal()" title="Create new case">+</button>
-            <button class="btn-case-settings" onclick="app.toggleCaseSettings()" title="Case settings">&#x2699;</button>
+            <!-- "New or link a case…" and "Case settings…" are the last two rows of
+                 the case picker's own list (CASE_PICKER_ACTIONS, session-ui.js); the
+                 "+" and gear buttons that sat here were removed (owner, 1.36.0). -->
             <div class="case-settings-popover hidden" id="caseSettingsPopover">
               <label class="checkbox-inline">
                 <input type="checkbox" id="caseAgentTeams" onchange="app.onCaseSettingChanged()">