Add signal attenuation knob to oscilloscope control panel

8-position volume control (5%-40%, default 20%) between Source
and Vertical sections. Persists via localStorage, keyboard
accessible, speech volume scales proportionally.

docs/src/components/OscilloscopeDisplay.astro

@@ -58,6 +58,14 @@
         <span class="scope-knob-label scope-source-name" id="scope-source-name">Spirals</span>
       </div>
 
+      <!-- LEVEL / ATTENUATION section -->
+      <div class="scope-section">
+        <span class="scope-section-label">Level</span>
+        <div class="scope-knob scope-volume-knob" id="scope-volume-knob"
+             role="button" tabindex="0" aria-label="Signal attenuation level"></div>
+        <span class="scope-knob-label scope-volume-label" id="scope-volume-label">20%</span>
+      </div>
+
       <!-- VERTICAL section -->
       <div class="scope-section">
         <span class="scope-section-label">Vertical</span>
@@ -126,8 +134,8 @@
 
   // ── Skin configuration ────────────────────────────────────
   const SKINS: Record<string, { brand: string; model: string; sub: string; sections: string[] }> = {
-    '465':  { brand: 'Tektronix', model: 'mcltspice',   sub: '',             sections: ['Source', 'Vertical', 'Horizontal', 'Trigger'] },
-    '545a': { brand: 'Tektronix', model: 'Type 545A',   sub: 'Oscilloscope', sections: ['Input', 'Vert Ampl', 'Sweep', 'Trigger'] },
+    '465':  { brand: 'Tektronix', model: 'mcltspice',   sub: '',             sections: ['Source', 'Level', 'Vertical', 'Horizontal', 'Trigger'] },
+    '545a': { brand: 'Tektronix', model: 'Type 545A',   sub: 'Oscilloscope', sections: ['Input', 'Atten', 'Vert Ampl', 'Sweep', 'Trigger'] },
   };
   const SKIN_ORDER = Object.keys(SKINS);
 
@@ -441,6 +449,45 @@
     ctx.fill();
   }
 
+  // ── Volume / attenuation control ─────────────────────────
+  function initVolume() {
+    const knob = document.getElementById('scope-volume-knob');
+    const label = document.getElementById('scope-volume-label');
+    const audio = document.getElementById('scope-audio') as HTMLAudioElement | null;
+    if (!knob || !label || !audio) return;
+    if (knob.dataset.volumeInit) return;
+    knob.dataset.volumeInit = 'true';
+
+    const LEVELS = [0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40];
+
+    let levelIndex = parseInt(localStorage.getItem('scope-volume') || '3', 10);
+    if (levelIndex < 0 || levelIndex >= LEVELS.length) levelIndex = 3;
+
+    function applyLevel(idx: number) {
+      levelIndex = idx;
+      const vol = LEVELS[idx];
+      audio!.volume = vol;
+      label!.textContent = `${Math.round(vol * 100)}%`;
+      const rotation = (idx / LEVELS.length) * 270 - 135;
+      knob!.style.setProperty('--knob-rotation', `${rotation}deg`);
+      localStorage.setItem('scope-volume', String(idx));
+    }
+
+    knob.addEventListener('click', () => {
+      applyLevel((levelIndex + 1) % LEVELS.length);
+    });
+
+    knob.addEventListener('keydown', (e: Event) => {
+      const ke = e as KeyboardEvent;
+      if (ke.key === 'Enter' || ke.key === ' ') {
+        ke.preventDefault();
+        applyLevel((levelIndex + 1) % LEVELS.length);
+      }
+    });
+
+    applyLevel(levelIndex);
+  }
+
   // ── Outer Limits easter egg ──────────────────────────────
   function initOuterLimits() {
     const knobs = document.querySelectorAll('.scope-easter-knob');
@@ -493,7 +540,8 @@
       utterance = new SpeechSynthesisUtterance(text);
       utterance.rate = 0.85;
       utterance.pitch = 0.7;
-      utterance.volume = 0.8;
+      const audio = document.getElementById('scope-audio') as HTMLAudioElement | null;
+      utterance.volume = Math.min(0.8, (audio?.volume ?? 0.2) * 2);
 
       // Prefer a deep English voice if available
       const voices = window.speechSynthesis.getVoices();
@@ -546,6 +594,7 @@
   function initAll() {
     initSkin();
     initScope();
+    initVolume();
     initOuterLimits();
   }
 

docs/src/styles/oscilloscope.css

@@ -261,6 +261,35 @@
   outline-offset: 2px;
 }
 
+/* ── Volume / attenuation knob (interactive) ──────────── */
+.scope-volume-knob {
+  cursor: pointer;
+  transition: transform 0.15s;
+  transform: rotate(var(--knob-rotation, 0deg));
+}
+
+.scope-volume-knob:hover {
+  transform: rotate(var(--knob-rotation, 0deg)) scale(1.08);
+}
+
+.scope-volume-knob:active {
+  transform: rotate(var(--knob-rotation, 0deg)) scale(0.95);
+}
+
+.scope-volume-knob:focus-visible {
+  outline: 2px solid var(--scope-teal);
+  outline-offset: 2px;
+}
+
+/* ── Volume label ─────────────────────────────────────── */
+.scope-volume-label {
+  max-width: 60px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  text-align: center;
+}
+
 /* ── Signal name label ──────────────────────────────────── */
 .scope-source-name {
   max-width: 60px;