refactor(ui): link event-log disclosure with aria-controls

Add aria-controls to the right-rail event-log collapse toggle pointing at
the log region, and title-case the settings label for consistency.

src/ui/RightRail.tsx

@@ -31,6 +31,7 @@ export function RightRail() {
           <button
             type="button"
             aria-expanded={logOpen}
+            aria-controls="right-rail-event-log"
             onClick={() => setLogOpen((prev) => !prev)}
             className="mb-3 flex w-full items-center justify-between font-semibold text-slate-400 text-xs tracking-wider uppercase hover:text-slate-300"
           >
@@ -39,7 +40,7 @@ export function RightRail() {
               {logOpen ? '▾' : '▸'}
             </span>
           </button>
-          {logOpen && <EventLog />}
+          <div id="right-rail-event-log">{logOpen && <EventLog />}</div>
         </div>
       )}
     </div>

src/ui/SettingsPanel.tsx

@@ -84,7 +84,7 @@ export function SettingsPanel() {
         <div className="flex flex-col gap-2 rounded-xl border border-slate-800 bg-slate-900/40 p-5">
           <label className="flex cursor-pointer items-center justify-between gap-4">
             <div className="flex flex-col">
-              <span className="font-semibold text-slate-200 text-sm">Show event log</span>
+              <span className="font-semibold text-slate-200 text-sm">Show Event Log</span>
               <span className="text-slate-400 text-xs">
                 Display the scrollable event log in the right rail and on mobile.
               </span>