feat(bank_panel): docked bank grid with LICE waveform thumbnails (M5 Wave A)

Docked SWELL window toggled by a new action, drawing the current bank as
per-sample min/max thumbnails (PCM_source + peaks) with an in-memory cache.
Pure grid-layout/cache-key math in bank_grid (tested). Renames peaks::Sample
-> AudioSample to avoid colliding with bank_model::Sample.

src/bank_panel.h

@@ -0,0 +1,41 @@
+#pragma once
+// bank_panel — the docked grid window (M5, Wave A). REAPER-facing shell: it owns
+// a SWELL dialog docked via DockWindowAddEx, and paints the current project's
+// bank as a grid of LICE-drawn waveform thumbnails. Read-only this wave: it NEVER
+// inserts into the arrange or mutates the project/bank (CONTEXT.md §load-bearing
+// principle). Audition / multi-select / keyboard nav are Wave B.
+//
+// The header is REAPER-free as practical: main.cpp drives the panel through these
+// free functions, passing the live session so the panel reads the current bank.
+// All SWELL / LICE / PCM_source use is confined to bank_panel.cpp. The pure
+// layout math and cache keys live in bank_grid (unit-tested outside the DAW).
+
+namespace reasampler {
+
+class ReaSamplerSession;
+
+// Wires the panel into main.cpp's lifecycle. Called once after the API pointers
+// are loaded, BEFORE the toggle action is registered. `session` must outlive the
+// panel (it is the extension-lifetime g_session). Stores the session pointer the
+// panel reads on every repaint; does not create the window yet.
+void bankPanelInit(ReaSamplerSession* session);
+
+// Toggles the docked window: creates+docks it if hidden, hides+undocks it if
+// shown. Bound to the "toggle bank panel" action. Safe to call before the first
+// timer tick.
+void bankPanelToggle();
+
+// Whether the panel window is currently open/visible. Feeds the action's
+// checked-state (toggleaction) so REAPER shows a tick next to the menu entry.
+bool bankPanelIsOpen();
+
+// Requests a repaint if the bank changed since the last paint (generation bump).
+// Cheap when nothing changed. Driven by the timer so a capture / project load is
+// reflected without the panel diffing the bank itself.
+void bankPanelRefresh();
+
+// 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();
+
+} // namespace reasampler