P3: unify connector layout + BSDL behind one PinModel provider

New PinModel interface (spec_for / layout / source) + a single apply_model(
Part*, const PinModel&) that materialises missing layout pins and sets each
pin's spec only where the model speaks (spec.source != None), so one source
never clobbers another's. ConnectorModel wraps pin_role/pin_layout;
BsdlPinModel wraps a parsed BsdlModel (indexed by port name and physical pad).
set-connector-type and screen_settype now use ConnectorModel + apply_model;
attach-bsdl and the restore re-apply keep calling apply_bsdl, now a thin
adapter over apply_model. Behaviour-preserving: unit tests (73 cases) green and
the real 8-card system re-runs identically (1517/1517 bound, same JTAG
findings). Covered by test_pin_model.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/system/pin_model.hpp

@@ -0,0 +1,55 @@
+#ifndef _PIN_MODEL_HPP_
+#define _PIN_MODEL_HPP_
+
+#include "pin_spec.hpp"
+
+#include <string>
+#include <utility>
+#include <vector>
+
+class Part;
+
+// A source of *expected* pin attributes for a part — a connector layout, a BSDL
+// device, (later) a SPICE/Modelica model. Both of today's sources implement this
+// interface and feed the single `apply_model()`, so `verify` stays agnostic of
+// where a pin's spec came from.
+struct PinModel {
+    virtual ~PinModel() = default;
+
+    // Expected spec for the pin identified by `pin_name` — its logical name, and
+    // for models that index physical pads, its package ball too. Returns a
+    // default PinSpec (source == None) when the model has nothing to say.
+    virtual PinSpec spec_for(const std::string &pin_name) const = 0;
+
+    // Canonical full pin-name list, used to materialise pins absent from the
+    // imported netlist. Empty means the model does not drive materialisation.
+    virtual std::vector<std::string> layout() const = 0;
+
+    // Which source this model represents (recorded in each spec it sets).
+    virtual SpecSource source() const = 0;
+};
+
+struct ApplyReport {
+    int pins_total = 0;    ///< pins on the part after materialisation
+    int set = 0;           ///< pins whose spec the model set
+    int materialised = 0;  ///< pins created from layout()
+};
+
+// Materialise the layout pins missing from the part, then set each pin's `spec`
+// from the model — only where the model actually speaks for that pin
+// (`spec.source != None`), so a model never wipes another source's spec.
+ApplyReport apply_model(Part *part, const PinModel &model);
+
+// Connector-layout model: wraps `pin_role(kind, name)` / `pin_layout(kind)`.
+class ConnectorModel : public PinModel {
+public:
+    explicit ConnectorModel(std::string kind) : kind_(std::move(kind)) {}
+    PinSpec spec_for(const std::string &pin_name) const override;
+    std::vector<std::string> layout() const override;
+    SpecSource source() const override { return SpecSource::ConnectorModel; }
+
+private:
+    std::string kind_;
+};
+
+#endif // _PIN_MODEL_HPP_