Fix SWELL drag guard, channel-fork the VST editor window class, dedupe own-module match

Panel drag no longer misfires on SWELL's always-zero wParam; stable/beta VST editors register distinct window classes against their own module instead of colliding on REAPER's; own-module basename matching moves to a tested pure helper.

src/shell/panel/CLAUDE.md

@@ -2,9 +2,9 @@
 
 ## Scope
 
-The REAPER-facing shell for the docked bank panel: the eight `bank_panel` split TUs
+The REAPER-facing shell for the docked bank panel: the nine `bank_panel` split TUs
 (`panel_window` / `panel_layout` / `panel_render` / `panel_input` / `panel_drag` /
-`panel_thumbnails` / `panel_audition` / `panel_bank_ops`, sharing state via
+`panel_drag_os` / `panel_thumbnails` / `panel_audition` / `panel_bank_ops`, sharing state via
 `panel_state.h`), plus `draw_kit`, the shared LICE draw shell also consumed by the
 VST3 editor (`shell/instrument/`).
 
@@ -47,12 +47,13 @@ live in `shell/bank_ops`, a sibling directory, not here.
 
 ## Modules
 
-- `bank_panel` (`shell/panel/`: `panel_window` / `panel_layout` / `panel_render` / `panel_input` / `panel_drag` / `panel_thumbnails` / `panel_audition` / `panel_bank_ops`, sharing state via `panel_state.h` — Q-W2 split of the former god-module into eight TUs) — docked LICE-drawn grid with three-zone layout: top toolbar (Capture → Placement, frequent acts only, via `action_bar`, short labels; Maintenance and the rarer Placement/Capture variants sit in the More (⋯) overflow menu via `overflow_menu`), bottom toolbar (four opposite-mode tag buttons + Show Both), and footer (`[Arrange|Design]` toggle, Tail button, Prune via `footer_bar`). Grid renders in sparse slot order with gap cells, drop dispatch, metadata overlay, and selection via `accent/tertiary` purple border. Draws through the L1 kit by palette role; OS drag-out via `drag_out` + `drag_out_win`. `panel_window` owns the SWELL dialog lifecycle + dialog proc + drop-target opt-in; `panel_layout` the toolbar/footer/menu rects + vertical-split geometry (the one geometry source both paint and hit-test read); `panel_render` the WM_PAINT draw; `panel_input` click/wheel/keyboard routing + the new-content auto-tag timer; `panel_drag` the hover + card-drag state machine + drop dispatch; `panel_thumbnails` the PCM→envelope thumbnail cache + the bank-change fingerprint pass; `panel_audition` the preview-playback engine; `panel_bank_ops` the menu/prompt UX skin over the promptless `shell/bank_ops` verbs. `draw_kit` (shared with the VST3 editor) stays a separate TU.
+- `bank_panel` (`shell/panel/`: `panel_window` / `panel_layout` / `panel_render` / `panel_input` / `panel_drag` / `panel_drag_os` / `panel_thumbnails` / `panel_audition` / `panel_bank_ops`, sharing state via `panel_state.h` — Q-W2 split of the former god-module into nine TUs) — docked LICE-drawn grid with three-zone layout: top toolbar (Capture → Placement, frequent acts only, via `action_bar`, short labels; Maintenance and the rarer Placement/Capture variants sit in the More (⋯) overflow menu via `overflow_menu`), bottom toolbar (four opposite-mode tag buttons + Show Both), and footer (`[Arrange|Design]` toggle, Tail button, Prune via `footer_bar`). Grid renders in sparse slot order with gap cells, drop dispatch, metadata overlay, and selection via `accent/tertiary` purple border. Draws through the L1 kit by palette role; OS drag-out via `drag_out` + `drag_out_win`. `panel_window` owns the SWELL dialog lifecycle + dialog proc + drop-target opt-in; `panel_layout` the toolbar/footer/menu rects + vertical-split geometry (the one geometry source both paint and hit-test read); `panel_render` the WM_PAINT draw; `panel_input` click/wheel/keyboard routing + the new-content auto-tag timer; `panel_drag` the hover + card-drag state machine + drop dispatch; `panel_drag_os` the OS hand-off/resume seam split out of `panel_drag`; `panel_thumbnails` the PCM→envelope thumbnail cache + the bank-change fingerprint pass; `panel_audition` the preview-playback engine; `panel_bank_ops` the menu/prompt UX skin over the promptless `shell/bank_ops` verbs. `draw_kit` (shared with the VST3 editor) stays a separate TU.
   - `panel_window` — SWELL dialog lifecycle + dialog proc + drop-target opt-in. The drop splits by extension: a `.rsbank` is a whole bank and routes to the package-import action (one NEW bank each), everything else keeps the audio-ingest route.
   - `panel_layout` — toolbar/footer/menu rects + vertical-split geometry (the one geometry source both paint and hit-test read).
   - `panel_render` — the WM_PAINT draw.
   - `panel_input` — click/wheel/keyboard routing + the new-content auto-tag timer.
   - `panel_drag` — the hover + card-drag state machine + drop dispatch.
+  - `panel_drag_os` — the OS hand-off/resume seam: the live re-ask the OS drag loop uses, the hand-off itself, and resuming the internal drag when the OS loop gives the gesture back.
   - `panel_thumbnails` — the PCM→envelope thumbnail cache + the bank-change fingerprint pass.
   - `panel_audition` — the preview-playback engine.
   - `panel_bank_ops` — the menu/prompt UX skin over the promptless `shell/bank_ops` verbs.