feat(toolbox, dialog): remove_data_source slot + WidgetData list-item colors

Two related ABI additions for the upcoming Filter Editor toolbox panel:

1. remove_data_source runtime-host slot
   Add an optional tail slot remove_data_source(handle) to
   PJ_toolbox_runtime_host_vtable_t so a toolbox can drop a data source
   it created via create_data_source — closes the create/notify/remove
   triangle on the toolbox runtime host. Currently the immediate driver
   is the Mosaico Cancel path, which already flags the gap in
   mosaico_dialog.cpp; the slot also unblocks toolbox_filter_editor's
   Reset flow on the staged write path.

2. WidgetData setListItemColors / listItemColors
   Add a per-item foreground-color channel to the WidgetData dialog
   protocol so plugins (concretely the Filter Editor dialog) can color
   source-list entries to match the curve colors in the plot. Mirrored
   by the host in widget_data_view so the dialog engine can read it
   back when rebuilding the Qt model.

ABI: both are tail-appended optional additions, no field reorder, no
struct shrink. ToolboxRuntimeHostView::removeDataSource() guards the
read with PJ_HAS_TAIL_SLOT; older hosts no-op for the new slot and
older plugins ignore it. WidgetData additions follow the same
backward-compatible pattern.

Test plan
- abidiff against baseline reports additions only.
- Existing toolbox_plugin_test builds and passes; the host vtable
  initializer gains .remove_data_source = nullptr.
- Downstream plugin (Filter Editor) consumes both additions in
  pj-official-plugins#141 + PlotJuggler/PJ4#160.

Author: pabloinigoblasco

pj_base/include/pj_base/sdk/toolbox_plugin_base.hpp

@@ -56,6 +56,14 @@ class ToolboxRuntimeHostView {
     }
   }
 
+  /// Ask the host to remove a data source this toolbox created (its derived
+  /// topics leave the catalog). No-op on hosts that predate this slot.
+  void removeDataSource(PJ_data_source_handle_t handle) const {
+    if (valid() && PJ_HAS_TAIL_SLOT(PJ_toolbox_runtime_host_vtable_t, host_.vtable, remove_data_source)) {
+      host_.vtable->remove_data_source(host_.ctx, handle);
+    }
+  }
+
   [[nodiscard]] const PJ_toolbox_runtime_host_t& raw() const {
     return host_;
   }

pj_base/include/pj_base/toolbox_protocol.h

@@ -74,6 +74,19 @@ typedef struct PJ_toolbox_runtime_host_vtable_t {
 
   /** [thread-safe] Notify the host that data has been modified; host refreshes UI. */
   void (*notify_data_changed)(void* ctx) PJ_NOEXCEPT;
+
+  /* ====================================================================
+   * Tail slots beyond here are OPTIONAL (added after v4.0). Plugins MUST
+   * guard reads via PJ_HAS_TAIL_SLOT(struct_size + nullability).
+   * ==================================================================== */
+
+  /** [thread-safe] Remove a data source the toolbox previously created via the
+   *  write host's create_data_source, so its derived topics disappear from the
+   *  host catalog — a clean reset that leaves no residue. The host tombstones
+   *  the data source's topics; cached reader handles are not invalidated.
+   *  Optional tail slot: hosts may omit it, so plugins guard with
+   *  PJ_HAS_TAIL_SLOT(PJ_toolbox_runtime_host_vtable_t, vtable, remove_data_source). */
+  void (*remove_data_source)(void* ctx, PJ_data_source_handle_t handle) PJ_NOEXCEPT;
 } PJ_toolbox_runtime_host_vtable_t;
 
 typedef struct {

pj_plugins/dialog_protocol/include/pj_plugins/host/widget_data_view.hpp

@@ -75,6 +75,9 @@ class WidgetDataView {
   [[nodiscard]] std::optional<std::vector<std::string>> selectedItems(std::string_view name) const {
     return getStringArray(name, "selected_items");
   }
+  [[nodiscard]] std::optional<std::vector<std::string>> listItemColors(std::string_view name) const {
+    return getStringArray(name, "list_item_colors");
+  }
 
   // --- QTableWidget ---
   [[nodiscard]] std::optional<std::vector<std::string>> tableHeaders(std::string_view name) const {

pj_plugins/dialog_protocol/include/pj_plugins/sdk/widget_data.hpp

@@ -93,6 +93,14 @@ class WidgetData {
     return *this;
   }
 
+  // Set foreground colors for QListWidget items, parallel to the items vector
+  // set by setListItems. Each entry is a CSS color string (e.g. "#ff0000") or
+  // empty to use the default palette color. Size must match the items vector.
+  WidgetData& setListItemColors(std::string_view name, const std::vector<std::string>& colors) {
+    entry(name)["list_item_colors"] = colors;
+    return *this;
+  }
+
   // --- QTableWidget ---
   WidgetData& setTableHeaders(std::string_view name, const std::vector<std::string>& headers) {
     entry(name)["headers"] = headers;

pj_plugins/tests/toolbox_plugin_test.cpp

@@ -103,6 +103,7 @@ PJ_toolbox_runtime_host_t makeRuntimeHost(RuntimeState* state) {
       .struct_size = sizeof(PJ_toolbox_runtime_host_vtable_t),
       .report_message = rhReportMessage,
       .notify_data_changed = rhNotifyDataChanged,
+      .remove_data_source = nullptr,
   };
   return PJ_toolbox_runtime_host_t{.ctx = state, .vtable = &vtable};
 }