refactor(capture): expose offline tail as docked-panel toggle

Replace the ...-with-tail variant actions with a pure tail_control module +
a docked-panel footer toggle (Off/Auto/Manual) read by CAPTURE_ITEM/TRACK.
Default None (byte-identical); Manual fixed 2s, in-memory session lifetime.
Tail mechanism unchanged; retired the variant ids.

src/bank_panel.h

@@ -13,6 +13,8 @@
 #include <string>
 #include <vector>
 
+#include "tail_control.h"  // TailSetting — the panel's tail-mode toggle state
+
 namespace reasampler {
 
 class ReaSamplerSession;
@@ -48,6 +50,17 @@ std::vector<std::string> bankPanelSelectedSampleIds();
 // reflected without the panel diffing the bank itself.
 void bankPanelRefresh();
 
+// The panel's current tail-mode setting (mode + Manual length), read by the plain
+// CAPTURE_ITEM / CAPTURE_TRACK actions when building a CaptureRequest so a capture
+// applies whatever the panel toggle is set to. Default None (exact bounds) — a
+// capture with no explicit choice stays byte-identical to today. Extension-session
+// setting: persists across project loads and panel open/close within a REAPER session;
+// resets to None only when the extension unloads (fresh REAPER session). Project
+// persistence across REAPER restarts is a noted follow-on.
+// Safe to call before the panel has ever opened (returns the default). READ of panel
+// state only; the toggle is mutated by a click inside the panel, never here.
+TailSetting bankPanelTailSetting();
+
 // Tears the panel down on extension unload: destroys the window and releases any
 // cached thumbnails / PCM handles. Mirror of bankPanelInit; safe if never opened.
 void bankPanelShutdown();