Fix catastrophic targets query and remove emoji from night mode buttons

The seasonal peak subquery used a correlated SELECT inside a GROUP BY,
causing a full nightly_cache scan per object (210-270s for 14k objects).
Replaced with a simple MAX() GROUP BY — now instant.

Also added three indexes on nightly_cache(night_date) that were missing
and causing all dashboard queries to run 2+ second full table scans.

Replaced 🔴 emoji in night mode buttons with CSS circles.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -49,7 +49,6 @@ export function BottomNav() {
           background: on ? 'rgba(160,0,0,0.85)' : 'var(--bg-panel)',
           border: `1px solid ${on ? '#800000' : 'var(--border)'}`,
           color: on ? '#ff6666' : 'var(--text-lo)',
-          fontSize: 16,
           display: 'none', // shown by .bottom-nav display:flex breakpoint via CSS class
           alignItems: 'center',
           justifyContent: 'center',
@@ -59,7 +58,12 @@ export function BottomNav() {
         }}
         className="night-fab"
       >
-        🔴
+        <span style={{
+          display: 'inline-block', width: 10, height: 10, borderRadius: '50%',
+          background: on ? '#ff4444' : 'var(--text-lo)',
+          boxShadow: on ? '0 0 6px #ff4444' : 'none',
+          transition: 'all 0.3s',
+        }} />
       </button>
       <nav className="bottom-nav">
         {navItems.map(item => (
@@ -192,7 +196,12 @@ export default function Sidebar() {
             letterSpacing: '0.06em', transition: 'all 0.2s',
           }}
         >
-          <span style={{ fontSize: 13 }}>🔴</span>
+          <span style={{
+            display: 'inline-block', width: 8, height: 8, borderRadius: '50%',
+            background: nightOn ? '#ff4444' : 'var(--text-lo)',
+            boxShadow: nightOn ? '0 0 5px #ff4444' : 'none',
+            flexShrink: 0, transition: 'all 0.2s',
+          }} />
           {nightOn ? 'Exit Night Mode' : 'Night Mode'}
         </button>
       </div>