feat(collab): cross-app selection — eeschema symbol ⇄ pcbnew footprint ghost highlight (collab-presence 0006)

Selecting a symbol in eeschema ghost-highlights the linked footprint(s) in
every pcbnew tab of the project, and vice versa — across users AND one
user's own two tabs. Native KIWAY cross-probe is inert in WASM (one frame
per page); this rides the presence layer instead.

- cross-app.ts: project-wide awareness-only room (presenceRoomId), publishes
  full PresenceState at selection rate (cursor always null); peers() = other-
  TOOL clients incl. own user's other tabs; window.__pcbjamCrossApp test handle
- presence-kicad.ts: parseSelectionEmit (bare array | {uuids,fpPaths}),
  xselFromPeerState (pcbnew paths → symbol uuids; eeschema uuids verbatim),
  cross peers appended to the kicadCollabSetRemote snapshot as
  {id "<user>#x<client>", name "<user> · sch|pcb", xsel}
- C++ (zero fork changes): pcbnew emits {uuids, fpPaths} (FOOTPRINT::GetPath)
  and ghost-renders xsel via path-tail suffix scan; eeschema resolves xsel via
  ResolveItem gated to the CURRENT sheet (xsel arrives project-wide, unlike
  room-scoped selections); ghostStyle = alphas × xselAlphaScale (0.55, tuner-
  patchable); new exports kicadCollabGetSelectionFull / TestGetCrossMapped /
  TestSelectComponent (skips power symbols — PWR_FLAG has no footprint) +
  merged-image dispatch
- tests: presence suites extended (payload shape, ghost render pixel tests,
  13/13) + new two-tab tests/web/cross-probe.spec.ts (passing vs real
  partykit); eeschema pixel compares now target the #glcanvas-* GAL panel
  (the whole-window #canvas compare flaked on the auto-dismissing version
  infobar — also fixes the long-known presence-eeschema restore flake);
  cross-app + presence-kicad vitest suites

Spec: docs/features/collab-presence/0006 (closed repo).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lg5jwWuhFH5dL8hEcBDuP2

wasm/bindings/kicad_editor_embind.cpp

@@ -55,6 +55,10 @@ std::string pcbCollabTestListItems( int aCount );
 std::string pcbCollabTestDemoSet();
 std::string pcbCollabGetViewport();
 std::string pcbCollabGetSelection();
+// Cross-app selection (collab-presence 0006).
+std::string pcbCollabGetSelectionFull();
+std::string pcbCollabTestGetCrossMapped();
+std::string pcbCollabTestSelectComponent();
 std::string pcbCollabTestSelectFirst();
 bool        pcbCollabTestClearSelection();
 
@@ -77,6 +81,10 @@ std::string schCollabTestListItems( int aCount );
 std::string schCollabTestDemoSet();
 std::string schCollabGetViewport();
 std::string schCollabGetSelection();
+// Cross-app selection (collab-presence 0006).
+std::string schCollabGetSelectionFull();
+std::string schCollabTestGetCrossMapped();
+std::string schCollabTestSelectComponent();
 std::string schCollabTestSelectFirst();
 bool        schCollabTestClearSelection();
 
@@ -204,6 +212,21 @@ static std::string collabGetSelection()
     return pcbEditorActive() ? pcbCollabGetSelection() : schCollabGetSelection();
 }
 
+static std::string collabGetSelectionFull()
+{
+    return pcbEditorActive() ? pcbCollabGetSelectionFull() : schCollabGetSelectionFull();
+}
+
+static std::string collabTestGetCrossMapped()
+{
+    return pcbEditorActive() ? pcbCollabTestGetCrossMapped() : schCollabTestGetCrossMapped();
+}
+
+static std::string collabTestSelectComponent()
+{
+    return pcbEditorActive() ? pcbCollabTestSelectComponent() : schCollabTestSelectComponent();
+}
+
 static std::string collabTestSelectFirst()
 {
     return pcbEditorActive() ? pcbCollabTestSelectFirst() : schCollabTestSelectFirst();
@@ -241,6 +264,10 @@ EMSCRIPTEN_BINDINGS(kicad_editor) {
     function("kicadCollabTestDemoSet", &collabTestDemoSet);
     function("kicadCollabGetViewport", &collabGetViewport);
     function("kicadCollabGetSelection", &collabGetSelection);
+    // Cross-app selection (collab-presence 0006).
+    function("kicadCollabGetSelectionFull", &collabGetSelectionFull);
+    function("kicadCollabTestGetCrossMapped", &collabTestGetCrossMapped);
+    function("kicadCollabTestSelectComponent", &collabTestSelectComponent);
     function("kicadCollabTestSelectFirst", &collabTestSelectFirst);
     function("kicadCollabTestClearSelection", &collabTestClearSelection);
 }