feat(pl_editor): Yjs collaborative bridge — differ/apply + generic reconciler (yjs-bridge commit 2)

Bidirectional bridge between pl_editor's DS_DATA_MODEL and a Yjs doc, two same-origin
tabs syncing over BroadcastChannel. Full architecture in features/yjs-bridge/0001-0002.

C++ (wasm layer, wasm/bindings/pl_editor_embind.cpp — public DS_DATA_MODEL API only,
zero added fork divergence beyond the OnModify hook):
- snapshot-differ ChangeSource: diff model vs last-emitted snapshot on OnModify,
  emit per-item delta JSON via EM_ASM window.kicadCollab.onDelta
- kicadCollabApply(json): apply remote delta by uuid — scalars (text/segment/rect)
  by field, polygon/bitmap via SetPageLayout-append blob; reseed snapshot + HardRedraw
- kicadCollabSnapshot() (seed/baseline), s_applyingRemote echo guard, and a
  kicadCollabTestAddText() PoC local-edit hook
- wire format: {added:[item],changed:[item],removed:[uuid]}, item = {id,type,...fields}

JS (web/apps/frontend/src/wasm/collab/, generic + schema-agnostic):
- reconciler: uuid-keyed Y.Map of per-item Y.Map; down = onDelta→Y, up = observe→apply,
  origin-tagged echo suppression; seed-once join adopts the doc authoritatively
- broadcast-transport: minimal BroadcastChannel Yjs provider (query/state catch-up)
- WasmTool wiring behind ?collab=1 (pl_editor only); gated debug logging

Tests: tests/kicad/pl_editor-collab.spec.ts — single-page C++ contract (snapshot/apply
changed+removed+added/echo-suppression) + two-tab BroadcastChannel A<->B propagation.
Reconciler+yjs bundled via esbuild (tests/collab/build.mjs, npm run build:collab).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/pnpm-lock.yaml

@@ -59,6 +59,9 @@ importers:
       tailwindcss-animate:
         specifier: ^1.0.7
         version: 1.0.7(tailwindcss@3.4.19(tsx@4.22.4))
+      yjs:
+        specifier: ^13.6.18
+        version: 13.6.31
       zod:
         specifier: ^3.24.1
         version: 3.25.76
@@ -1769,6 +1772,9 @@ packages:
     resolution: {integrity: sha512-6B3tLtFqtQS4ekarvLVMZ+X+VlvQekbe4taUkf/rhVO3d/h0M2rfARm/pXLcPEsjjMsFgrFgSrhQIxcSVrBz8w==}
     engines: {node: '>=18'}
 
+  isomorphic.js@0.2.5:
+    resolution: {integrity: sha512-PIeMbHqMt4DnUP3MA/Flc0HElYjMXArsw1qwJZcm9sqR8mq3l8NYizFMty0pWwE/tzIGH3EKK5+jes5mAr85yw==}
+
   jiti@1.21.7:
     resolution: {integrity: sha512-/imKNG4EbWNrVjoNC/1H5/9GFy+tqjGBHCaSsN+P2RnPqjsLmv6UD3Ej+Kj8nBWaRAwyk7kK5ZUc+OEatnTR3A==}
     hasBin: true
@@ -1795,6 +1801,11 @@ packages:
   jsonfile@6.2.1:
     resolution: {integrity: sha512-zwOTdL3rFQ/lRdBnntKVOX6k5cKJwEc1HdilT71BWEu7J41gXIB2MRp+vxduPSwZJPWBxEzv4yH1wYLJGUHX4Q==}
 
+  lib0@0.2.117:
+    resolution: {integrity: sha512-DeXj9X5xDCjgKLU/7RR+/HQEVzuuEUiwldwOGsHK/sfAfELGWEyTcf0x+uOvCvK3O2zPmZePXWL85vtia6GyZw==}
+    engines: {node: '>=16'}
+    hasBin: true
+
   light-my-request@5.14.0:
     resolution: {integrity: sha512-aORPWntbpH5esaYpGOOmri0OHDOe3wC5M2MQxZ9dvMLZm6DnaAn0kJlcbU9hwsQgLzmZyReKwFwwPkR+nHu5kA==}
 
@@ -2326,6 +2337,10 @@ packages:
   yallist@3.1.1:
     resolution: {integrity: sha512-a4UGQaWPH59mOXUYnAG2ewncQS4i4F43Tv3JoAM+s2VDAmS9NsK8GpDMLrCHPksFT7h3K6TOoUNn2pb7RoXx4g==}
 
+  yjs@13.6.31:
+    resolution: {integrity: sha512-Eq+5BRfbeGyqGVrTJL3bEcr8gKkxPuyuoHmAwpk52fDb8kOVMrfVSTRPd6yiGgX5Fskb96qCRjzjbRjrL4YEnw==}
+    engines: {node: '>=16.0.0', npm: '>=8.0.0'}
+
   zod@3.25.76:
     resolution: {integrity: sha512-gzUt/qt81nXsFGKIFcC3YnfEAx5NkunCfnDlvuBSSFS02bcXu4Lmea0AFIUwbLWxWPx3d9p8S5QoaujKcNQxcQ==}
 
@@ -3563,6 +3578,8 @@ snapshots:
 
   isexe@3.1.5: {}
 
+  isomorphic.js@0.2.5: {}
+
   jiti@1.21.7: {}
 
   js-tokens@4.0.0: {}
@@ -3583,6 +3600,10 @@ snapshots:
     optionalDependencies:
       graceful-fs: 4.2.11
 
+  lib0@0.2.117:
+    dependencies:
+      isomorphic.js: 0.2.5
+
   light-my-request@5.14.0:
     dependencies:
       cookie: 0.7.2
@@ -4083,4 +4104,8 @@ snapshots:
 
   yallist@3.1.1: {}
 
+  yjs@13.6.31:
+    dependencies:
+      lib0: 0.2.117
+
   zod@3.25.76: {}