feat(collab): presence P2 — pcbnew selection/cursor emit + remote VIEW_OVERLAY render (collab-presence 0002)

Zero kicad-fork changes — all in the embind layer:
- pcbnew_embind.cpp: presence section — canvas wx Bind() triggers (motion/
  leave/up/key/wheel) + COLLAB_LISTENER piggyback → post-settle selection
  check (dedupe) → onSelection; throttled cursor emit via VIEW::ToWorld;
  viewport push/pull (px-per-IU via the GAL matrix — GetScale() is the zoom
  and sized the first cut's overlay nm-small); kicadCollabSetRemote renders
  peers' cursors (cross + name) and selection bbox outlines into one
  per-user-colored VIEW_OVERLAY (CallAfter+COROUTINE), never touching local
  selection; PresenceStart/GetSelection/TestSelectFirst/TestClearSelection.
- kicad_editor_embind.cpp: merged-image dispatch (pcb-only until 0003).
- presence-kicad.ts: bindKicadPresence — routes emits into awareness (0001)
  and pushes trailing-throttled peer snapshots into the wasm; wired from
  WasmTool.startPresence (pcbnew-gated). +5 unit tests.
- tests/kicad/presence-pcbnew.spec.ts: 5 e2e — programmatic + real box-select
  emit, throttled cursor, remote render with no-leak + pixel restore,
  viewport unit band. Existing pcbnew-collab/items-bridge suites stay green.

Verified live: two tabs over partykit — peer cursor cross + label + selection
outline visible on the other tab's canvas.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CvqUd4QsJSGHN28aunJRTq

wasm/bindings/kicad_editor_embind.cpp

@@ -45,6 +45,13 @@ std::string pcbCollabTestMoveFirst( int aDx, int aDy );
 std::string pcbCollabGetPos( std::string aId );
 bool        pcbCollabTestRemoveItem( std::string aId );
 bool        pcbCollabTestRotateItem( std::string aId, double aDeg );
+// Presence (collab-presence 0002) — pcbnew only until 0003 adds the sch side.
+void        pcbCollabPresenceStart();
+void        pcbCollabSetRemote( std::string aJson );
+std::string pcbCollabGetViewport();
+std::string pcbCollabGetSelection();
+std::string pcbCollabTestSelectFirst();
+bool        pcbCollabTestClearSelection();
 
 bool        schEditorActive();
 void        schCollabApply( std::string aJson );
@@ -133,6 +140,41 @@ static bool collabTestRotateItem( std::string aId, double aDeg )
                              : schCollabTestRotateItem( aId, aDeg );
 }
 
+// Presence shims (collab-presence 0002): pcb-only for now — the sch frame no-ops /
+// returns empty until 0003 lands schCollab* counterparts, matching how the JS side
+// gates presence on the active tool.
+static void collabPresenceStart()
+{
+    if( pcbEditorActive() )
+        pcbCollabPresenceStart();
+}
+
+static void collabSetRemote( std::string aJson )
+{
+    if( pcbEditorActive() )
+        pcbCollabSetRemote( aJson );
+}
+
+static std::string collabGetViewport()
+{
+    return pcbEditorActive() ? pcbCollabGetViewport() : std::string();
+}
+
+static std::string collabGetSelection()
+{
+    return pcbEditorActive() ? pcbCollabGetSelection() : std::string( "[]" );
+}
+
+static std::string collabTestSelectFirst()
+{
+    return pcbEditorActive() ? pcbCollabTestSelectFirst() : std::string();
+}
+
+static bool collabTestClearSelection()
+{
+    return pcbEditorActive() ? pcbCollabTestClearSelection() : false;
+}
+
 
 EMSCRIPTEN_BINDINGS(kicad_editor) {
     // Programmatic file open (preferred over UI automation from the web app).
@@ -150,6 +192,13 @@ EMSCRIPTEN_BINDINGS(kicad_editor) {
     // endpoint, field text — flow from the per-editor blocks unchanged).
     function("kicadCollabTestRemoveItem", &collabTestRemoveItem);
     function("kicadCollabTestRotateItem", &collabTestRotateItem);
+    // Presence (collab-presence 0002).
+    function("kicadCollabPresenceStart", &collabPresenceStart);
+    function("kicadCollabSetRemote", &collabSetRemote);
+    function("kicadCollabGetViewport", &collabGetViewport);
+    function("kicadCollabGetSelection", &collabGetSelection);
+    function("kicadCollabTestSelectFirst", &collabTestSelectFirst);
+    function("kicadCollabTestClearSelection", &collabTestClearSelection);
 }
 
 #endif // __EMSCRIPTEN__