refactor: modal-gate helper + data-driven colormap table

Two extensibility easy-wins, both behavior-preserving:

- UiModalOpen() centralizes the "an overlay owns input" check that was
  copy-pasted as `!showFileBrowser && !showAbout` across 6 input gates.
  New overlays now update one place.
- Colormaps become a COLORMAPS[] table (name + function) indexed by enum.
  GetColormapColor and the sidebar both read it, so adding a colormap is
  one enum value + one Cmap* fn + one row — and the sidebar name can no
  longer drift from the enum (deleted the parallel colormapNames[] array).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/spectrogram.c

@@ -217,7 +217,7 @@ int main(int argc, char* argv[])
         }
         
         // File browser toggle
-        if (IsKeyPressed(KEY_O) && !app.showFileBrowser && !app.showAbout) {
+        if (IsKeyPressed(KEY_O) && !UiModalOpen()) {
             app.showFileBrowser = true;
             ScanDirectory(GetWorkingDirectory());
         }
@@ -258,7 +258,7 @@ int main(int argc, char* argv[])
         }
 
         // View controls
-        if (app.loaded && !app.showFileBrowser && !app.showAbout) {
+        if (app.loaded && !UiModalOpen()) {
             // Spectrogram area fills remaining window space (scaled)
             float viewScale = GetUIScale();
             float sidebarWidth = 320 * viewScale;
@@ -438,7 +438,7 @@ int main(int argc, char* argv[])
         }
 
         // Keyboard shortcuts (SPACE for play/stop toggle, ESC for clear)
-        if (IsKeyPressed(KEY_SPACE) && !app.showFileBrowser && !app.showAbout) {
+        if (IsKeyPressed(KEY_SPACE) && !UiModalOpen()) {
             if (app.isPlaying && AudioPlaybackSound.frameCount > 0) {
                 // Currently playing - stop it
                 StopSound(AudioPlaybackSound);
@@ -459,7 +459,7 @@ int main(int argc, char* argv[])
         }
 
         // Export PNG
-        if (IsKeyPressed(KEY_E) && !app.showFileBrowser && !app.showAbout && app.stftComputed) {
+        if (IsKeyPressed(KEY_E) && !UiModalOpen() && app.stftComputed) {
             ExportPNG(&app, app.exportDir);
         }
 
@@ -540,7 +540,7 @@ int main(int argc, char* argv[])
         }
 
         // LMB drag = box select (time + frequency) OR drag existing selection
-        if (app.loaded && !app.showFileBrowser && !app.showAbout && CheckCollisionPointRec(mousePos, selBounds)) {
+        if (app.loaded && !UiModalOpen() && CheckCollisionPointRec(mousePos, selBounds)) {
             // Set cursor to resize all when near divider
             if (mouseNearDivider && !app.isDividing) {
                 SetMouseCursor(MOUSE_CURSOR_RESIZE_ALL);
@@ -639,7 +639,7 @@ int main(int argc, char* argv[])
 
         // Handle divider drag. Works whether or not the scope is currently shown
         // (when hidden, the handle sits at the bottom and can be dragged back up).
-        if (app.loaded && !app.showFileBrowser && !app.showAbout) {
+        if (app.loaded && !UiModalOpen()) {
             // Grab the handle. The starting position is the *effective* divider,
             // which is the bottom of the view (1.0) while the scope is hidden.
             if (mouseNearDivider && IsMouseButtonPressed(MOUSE_LEFT_BUTTON)) {