chore(ui): L-shell step 7 — retire the dead #settings-overlay cruft (designer P3)

The settings MODAL backdrop (#settings-overlay) died when MCP connections moved to
the Manage > Connections pane (step 6) — the #settings-mcp-* content rules are
reused there, but the overlay wrapper is gone.  Remove the closed loop of dead-but-
mutually-alive references: the CSS rule, the stale "settings-overlay" modal-id
array entry, and the guarded getElementById no-op in the settings-close path.

The other fork-collapse dead-code (the getFocusedPane stub + its null-gated
branches, the partially-retired settings-gear) is woven into still-live handlers —
deferred to the merge-gate /review for a systematic sweep with the review findings.

Verified: 0 settings-overlay refs remain; node + prettier clean; CSS audit at
baseline; standalone harness errs:[].

turnstone/ui/static/app.js

@@ -1908,8 +1908,6 @@ function closeSettingsPanel() {
   if (inner && inner.style.display !== "none") {
     cancelRevokeMcp();
   }
-  const overlay = document.getElementById("settings-overlay");
-  if (overlay) overlay.style.display = "none";
   if (_settingsTrap) {
     document.removeEventListener("keydown", _settingsTrap);
     _settingsTrap = null;
@@ -2153,7 +2151,6 @@ document.addEventListener("keydown", function (e) {
     "edit-title-overlay",
     "delete-ws-overlay",
     "ws-delete-overlay",
-    "settings-overlay",
     "revoke-mcp-overlay",
   ];
   for (let mi = 0; mi < modalIds.length; mi++) {

turnstone/ui/static/style.css

@@ -2146,15 +2146,9 @@ audio.media-player {
 /* ==========================================================================
    Settings: MCP server connections
    ========================================================================== */
-#settings-overlay {
-  position: fixed;
-  inset: 0;
-  background: rgba(0, 0, 0, 0.6);
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  z-index: 1000;
-}
+/* (#settings-overlay — the old settings MODAL backdrop — retired: MCP connections
+   moved to the Manage > Connections pane, which provides its own container; the
+   #settings-mcp-* content rules below are reused live in that pane.) */
 #settings-mcp-loading,
 #settings-mcp-empty {
   color: var(--fg-dim);