feat: scroll the sidebar controls with the mouse wheel when they overflow

The left-hand control panel is laid out top-to-bottom with a running y; with
annotations expanded or a short window, the bottom buttons (export, signal
info, about) ran off the bottom and were unreachable. Offset the content by a
sidebarScroll amount, measure the laid-out height, and let the wheel scroll it
(clamped) when the cursor is over the sidebar and no modal is open. No visible
scrollbar; the spectrogram's wheel-zoom already ignores the sidebar column so
the two never both fire.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/spectrogram_types.h

@@ -187,6 +187,9 @@ typedef struct {
     // Overlays
     bool showAbout;  // About / help dialog
 
+    // Sidebar scroll offset (px), for when controls overflow a short window
+    float sidebarScroll;
+
     // File browser state
     bool showFileBrowser;
     char browserPath[512];

src/ui.c

@@ -336,11 +336,15 @@ void DrawSidebar(void)
     float scale = GetUIScale();
     float sidebarWidth = 300 * scale;
     float x = 10 * scale;
-    float y = 10 * scale;
+    float topMargin = 10 * scale;
+    // Content is laid out top-to-bottom from `y`; shift it up by the scroll
+    // offset so controls that overflow a short window can be reached. Clicks and
+    // sliders track automatically since their rects are derived from `y`.
+    float y = topMargin - app.sidebarScroll;
     int fontSize = (int)(12 * scale);
     bool needsRegen = false;
 
-    // Dark sidebar background
+    // Dark sidebar background (fixed; does not scroll)
     DrawRectangle(0, 0, (int)(sidebarWidth + 20 * scale), GetScreenHeight(), (Color){ 35, 35, 40, 255 });
     DrawLine((int)(sidebarWidth + 10 * scale), 0, (int)(sidebarWidth + 10 * scale), GetScreenHeight(), GRAY);
     
@@ -644,6 +648,25 @@ void DrawSidebar(void)
         ColorizeSpectrogram(&app.spectrogramImage, &app.spectrogramTexture);
         app.visibleTextureValid = false;  // Force cache invalidation
     }
+
+    // ---- Scroll handling ----
+    // `y` now sits at the bottom of the laid-out content (in screen space).
+    // Its natural position (scroll == 0) is y + sidebarScroll; allow scrolling
+    // until that bottom, plus a small pad, reaches the window's bottom edge.
+    float contentBottom = y + app.sidebarScroll;
+    float maxScroll = contentBottom + topMargin - GetScreenHeight();
+    if (maxScroll < 0) maxScroll = 0;
+
+    // Wheel scrolls the sidebar only when the cursor is over it and no modal is
+    // up. The spectrogram's own wheel-zoom already ignores the sidebar column,
+    // so the two never both fire.
+    bool overSidebar = GetMousePosition().x < (sidebarWidth + 20 * scale);
+    if (overSidebar && !UiModalOpen()) {
+        float wheel = GetMouseWheelMove();
+        if (wheel != 0.0f) app.sidebarScroll -= wheel * 40 * scale;
+    }
+    if (app.sidebarScroll > maxScroll) app.sidebarScroll = maxScroll;
+    if (app.sidebarScroll < 0.0f) app.sidebarScroll = 0.0f;
 }
 
 static void DrawSlider(Rectangle bounds, float value)