refactor(web): split into GPL standalone editor + thin reference backend

Reduce web/ to a single generic editor app plus a minimal example backend,
moving all project-specific/app code out to the closed root repo:

- apps/frontend -> standalone (@pcbjam/standalone): the GPL editor. Strips the
  project-management UI (ProjectsPage/ProjectDetailPage/UploadDropzone and the
  write half of lib/api.ts). WasmTool now takes fetchBytes + assetBaseUrl as
  injected props (decoupled from the API client) so it can be driven by either
  a backend or a local folder. New HomePage (local-folder loader + backend
  project list) and read-only ProjectView. BroadcastChannel collab unchanged.
- backend (@pcbjam/backend-example): thin Fastify+ts-rest reference impl of the
  @pcbjam/shared contract — serves a single project off the local filesystem
  (PROJECT_DIR), no DB/auth/uploads.
- packages/contract -> web/pcbjam-shared (git submodule, MIT @pcbjam/shared).
- Remove apps/server, packages/storage, packages/contract, docker-compose
  (server + storage move to the closed root repo; preserved via subtree
  branches). Rewrite pnpm-workspace/turbo/.env for the frontend-only layout.
- Add tests/fixtures/demo so the editor + example backend run out of the box.

Standalone typechecks + builds; backend serves the contract end-to-end.

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

web/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "kicad-web",
+  "name": "pcbjam-web",
   "version": "0.0.0",
   "private": true,
   "packageManager": "pnpm@10.33.0",
@@ -10,12 +10,7 @@
     "dev": "turbo run dev",
     "build": "turbo run build",
     "typecheck": "turbo run typecheck",
-    "lint": "turbo run lint",
-    "db:up": "docker compose up -d",
-    "db:down": "docker compose down",
-    "db:generate": "pnpm --filter @kicad-web/server db:generate",
-    "db:migrate": "pnpm --filter @kicad-web/server db:migrate",
-    "db:seed": "pnpm --filter @kicad-web/server db:seed"
+    "lint": "turbo run lint"
   },
   "devDependencies": {
     "turbo": "^2.5.0",