fix: flyout sheet title CSS, ARIA role correction, sidebar-delete cleanup

Fix A: Add .flyout-sheet__title CSS rule in style.css flyout-sheet section.
  - Kill confirm sheet renders a title div with class flyout-sheet__title
    but no CSS rule existed; title displayed as raw unstyled text.
  - Added padding/font/color/alignment rule after .flyout-sheet__handle.

Fix B: Change role='menuitem' to role='button' on Kill and Cancel buttons
  in _openMobileKillConfirm() (app.js).
  - Buttons inside a role='alertdialog' must use role='button' per ARIA spec;
    role='menuitem' is only valid inside role='menu'.

Fix C: Remove 3 orphaned .sidebar-delete CSS rule blocks from style.css.
  - .sidebar-delete, .sidebar-item:hover .sidebar-delete, .sidebar-delete:hover
    were dead code after the delete button was removed from buildSidebarHTML().

Tests added:
  - test_frontend_css.py: test_flyout_sheet_title_css_exists (Fix A)
  - test_frontend_js.py:  test_kill_confirm_buttons_use_role_button (Fix B)
  - test_frontend_css.py: test_no_sidebar_delete_css (Fix C)

muxplex/frontend/app.js

@@ -1738,8 +1738,8 @@ function _openMobileKillConfirm(sessionName, remoteId) {
   html += '<div class="flyout-sheet__panel" aria-label="Confirm kill session" role="alertdialog">';
   html += '<div class="flyout-sheet__handle" aria-hidden="true"></div>';
   html += '<div class="flyout-sheet__title">Kill ' + escapeHtml(sessionName) + '?</div>';
-  html += '<button class="flyout-sheet__item flyout-sheet__item--danger" data-action="confirm-kill" role="menuitem">Kill</button>';
+  html += '<button class="flyout-sheet__item flyout-sheet__item--danger" data-action="confirm-kill" role="button">Kill</button>';
-  html += '<button class="flyout-sheet__item" data-action="cancel" role="menuitem">Cancel</button>';
+  html += '<button class="flyout-sheet__item" data-action="cancel" role="button">Cancel</button>';
   html += '</div>';
 
   sheet.innerHTML = html;

muxplex/frontend/style.css

@@ -1156,33 +1156,6 @@ body {
 
 
 
-.sidebar-delete {
-  background: none;
-  border: none;
-  color: var(--text-dim);
-  font-size: 13px;
-  cursor: pointer;
-  padding: 1px 5px;
-  border-radius: 3px;
-  opacity: 0;
-  transition: opacity 150ms ease;
-  pointer-events: none;
-  flex-shrink: 0;
-  line-height: 1;
-}
-
-.sidebar-item:hover .sidebar-delete,
-.sidebar-item:focus-within .sidebar-delete {
-  opacity: 1;
-  pointer-events: auto;
-}
-
-.sidebar-delete:hover {
-  color: #ef4444;
-  background: rgba(239, 68, 68, 0.1);
-  opacity: 1;
-}
-
 /* ============================================================
    Header actions + settings buttons
    ============================================================ */
@@ -2432,6 +2405,14 @@ body {
   margin: 10px auto 6px;
 }
 
+.flyout-sheet__title {
+  padding: 8px 16px 12px;
+  font-size: 15px;
+  font-weight: 600;
+  color: var(--text);
+  text-align: center;
+}
+
 .flyout-sheet__item {
   display: flex;
   align-items: center;

muxplex/tests/test_frontend_css.py

@@ -2274,3 +2274,38 @@ def test_tile_delete_css_removed() -> None:
         ".tile-delete CSS rules must be removed from style.css — "
         "the button was removed from buildTileHTML; orphaned CSS is dead code"
     )
+
+
+# ── Fix A: .flyout-sheet__title CSS (Phase 3 COE re-verification) ─────────────
+
+
+def test_flyout_sheet_title_css_exists() -> None:
+    """.flyout-sheet__title must have a CSS rule in the flyout-sheet section.
+
+    Fix A: The kill-confirm sheet renders a title div with class
+    `flyout-sheet__title` but the CSS rule was missing, leaving the title
+    as raw unstyled text.
+    """
+    css = read_css()
+    assert ".flyout-sheet__title" in css, (
+        ".flyout-sheet__title CSS rule must exist in style.css — "
+        "the kill-confirm sheet renders a title div with this class"
+    )
+
+
+# ── Fix C: .sidebar-delete orphaned CSS removed (Phase 3 COE re-verification) ──
+
+
+def test_no_sidebar_delete_css() -> None:
+    """.sidebar-delete CSS rules must be removed from style.css (orphaned dead code).
+
+    Fix C: The .sidebar-delete button was removed from buildSidebarHTML() in a
+    previous task.  The 3 CSS rule blocks (.sidebar-delete,
+    .sidebar-item:hover .sidebar-delete, .sidebar-delete:hover) are now dead
+    code and must be cleaned up.
+    """
+    css = read_css()
+    assert ".sidebar-delete" not in css, (
+        ".sidebar-delete CSS rules must be removed from style.css — "
+        "the button was removed from buildSidebarHTML(); orphaned CSS is dead code"
+    )

muxplex/tests/test_frontend_js.py

@@ -4181,3 +4181,33 @@ def test_flyout_menu_map_is_const() -> None:
     assert "var FLYOUT_MENU_MAP" not in _JS, (
         "FLYOUT_MENU_MAP must not use 'var' — change to 'const'"
     )
+
+
+# ── Fix B: ARIA role correction in kill confirm sheet (Phase 3 COE re-verification) ──
+
+
+def test_kill_confirm_buttons_use_role_button() -> None:
+    """Kill and Cancel buttons inside the alertdialog must use role='button', not 'menuitem'.
+
+    Fix B: _openMobileKillConfirm() renders buttons inside a role='alertdialog'
+    panel.  The ARIA spec requires buttons inside an alertdialog to carry
+    role='button' (not role='menuitem', which only belongs inside role='menu').
+    """
+    # Negative check: role="menuitem" must NOT appear on the confirm-kill button
+    assert 'data-action="confirm-kill" role="menuitem"' not in _JS, (
+        "Kill button inside alertdialog must not use role='menuitem' — "
+        "use role='button' instead (menuitem is only valid inside role='menu')"
+    )
+    # Negative check: role="menuitem" must NOT appear on the cancel button
+    assert 'data-action="cancel" role="menuitem"' not in _JS, (
+        "Cancel button inside alertdialog must not use role='menuitem' — "
+        "use role='button' instead (menuitem is only valid inside role='menu')"
+    )
+    # Positive check: role="button" must appear on the confirm-kill button
+    assert 'data-action="confirm-kill" role="button"' in _JS, (
+        "Kill button inside alertdialog must use role='button'"
+    )
+    # Positive check: role="button" must appear on the cancel button
+    assert 'data-action="cancel" role="button"' in _JS, (
+        "Cancel button inside alertdialog must use role='button'"
+    )