L5: dock-panel button refinements — overflow menu, tooltips, opposite-mode tag buttons

Top-bar rare-capture variants move to a right-anchored More popup; short faces gain
hover-delay full-name tooltips (prefix stripped); bottom bar becomes four opposite-mode
Item/Track tag buttons + Show Both (Toggle/Activates dropped); wider cluster gaps. New
pure overflow_menu/mode_enable/tooltip modules, CTest-covered. Same actions, same contract.

src/overflow_menu.cpp

@@ -0,0 +1,42 @@
+// overflow_menu — pure implementation. See overflow_menu.h. NO REAPER / SWELL / LICE / vendor.
+
+#include "overflow_menu.h"
+
+namespace reasampler {
+
+int menuButtonReserve(const MenuBarRect& bar, const MenuButtonSpec& spec) {
+    if (bar.width <= 0 || bar.height <= 0 || spec.buttonWidth <= 0) return 0;
+    // The reserve is the button width plus a right gap (rightInset) and a matching left gap
+    // (also rightInset) so the frequent buttons have breathing room before the menu button.
+    return spec.buttonWidth + 2 * spec.rightInset;
+}
+
+MenuButtonRect computeMenuButton(const MenuBarRect& bar, const MenuButtonSpec& spec) {
+    MenuButtonRect btn;
+    if (bar.width <= 0 || bar.height <= 0 || spec.buttonWidth <= 0) return btn;
+
+    const int right = bar.x + bar.width - spec.rightInset;
+    const int left = right - spec.buttonWidth;
+    if (left < bar.x + spec.minLeftInset) return btn;  // too narrow — suppress
+
+    int top = bar.y + spec.verticalInset;
+    int height = bar.height - 2 * spec.verticalInset;
+    if (height <= 0) {  // thin band: clamp to the band's own extents rather than go negative
+        top = bar.y;
+        height = bar.height;
+    }
+
+    btn.x = left;
+    btn.y = top;
+    btn.width = spec.buttonWidth;
+    btn.height = height;
+    return btn;
+}
+
+bool hitTestMenuButton(int px, int py, const MenuButtonRect& button) {
+    if (button.empty()) return false;
+    return px >= button.x && px < button.x + button.width &&
+           py >= button.y && py < button.y + button.height;
+}
+
+} // namespace reasampler