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/mode_enable.h

@@ -0,0 +1,39 @@
+#pragma once
+// mode_enable — the REAPER-free opposite-mode enablement predicate behind the bank_panel BOTTOM
+// toolbar's four Item/Track × Arrange/Design tag buttons (Phase L, L5, refinement 3). Each tag
+// button sends the selection to a TARGET mode; a button is meaningful ONLY when its target is
+// the OPPOSITE of the currently active mode. When Design is active the two "…: Arrange" buttons
+// are live and the two "…: Design" buttons are dead (already there); when Arrange is active the
+// reverse. This module owns that one decision — (active mode, button target) -> live/disabled —
+// as a pure predicate, unit-tested for both active modes; the shell reads the active mode from
+// view().activeModeId() (the SAME source the footer toggle reads — one source of truth for
+// "which mode is active") and draws the disabled buttons in the kit Disabled state.
+//
+// Why pure: which button is live is a decision, not a draw or a DAW behaviour. Keeping it here
+// means the shell cannot drift the enablement from the rule, and both active modes are covered
+// by CTest, not only whichever one a manual DAW pass happened to sit in.
+//
+// PURE MODULE: NO REAPER types, NO SWELL, NO LICE, NO vendor/ includes. Standard library only.
+
+#include <string>
+
+namespace reasampler {
+
+// A tag button's TARGET mode — the mode it sends the selection to when fired. Arrange = the
+// untagged default (returning the selection to Arrange), Design = tagged into the Design mode.
+// The Item/Track axis is orthogonal to enablement (both Item and Track buttons for a target
+// enable/disable together), so it is NOT modelled here — the shell carries it per button.
+enum class TagTarget {
+    Arrange,
+    Design,
+};
+
+// True iff a tag button whose target is `target` should be LIVE (clickable), given the active
+// mode id `activeModeId` (as returned by ViewModeModel::activeModeId() — the mode ids are the
+// pure `kArrangeModeId` / `kDesignModeId` constants). The rule: a button is live iff its target
+// differs from the active mode — you tag INTO the mode you are not currently in. An unrecognized
+// active id (neither arrange nor design) leaves every button live (fail-open: never silently
+// disable an action the user can still reach), so a future added mode never dead-locks the bar.
+bool tagButtonEnabled(const std::string& activeModeId, TagTarget target);
+
+} // namespace reasampler