fix(e2e): let per-file E2E targets run without mock serve dependencies

Since #1710 the Playwright configs start the Stalker and Xtream mocks
themselves (`node --import tsx …`), so @nx/playwright can no longer map
those webServers to Nx tasks and infers the atomized `e2e-ci--*` targets
as non-parallel. The `e2e-ci--src/*.e2e.ts` target default still made
them depend on the continuous `stalker-mock-server:serve` and
`xtream-mock-server:serve` targets, and Nx refuses to run a
non-parallel task with continuous dependencies, so every per-file
target failed before running anything.

Drop the redundant mock dependencies and keep the Electron build.
The mock-launch guard spec now also rejects any nx.json target default
that depends on a mock-server task.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/xtream-mock-server.md

@@ -579,7 +579,10 @@ for the serve target's `--tsconfig` flag and is required for the `@iptvnator/*`
 path aliases. `project-config.spec.ts` pins which configs start which mock,
 and fails if any of them launches a mock through Nx or a new config starts one
 without being listed there. The `serve` targets remain the entry point
-for starting a mock by hand. The web-e2e `web-backend` entry uses the same
+for starting a mock by hand, and no E2E target may depend on them: with no
+Nx-launched server, `@nx/playwright` infers the atomized `e2e-ci--*` targets
+as non-parallel, and Nx refuses to run a non-parallel task that depends on a
+continuous `serve` task. The same spec guards `nx.json` `targetDefaults`. The web-e2e `web-backend` entry uses the same
 launch form; see [PWA web backend](pwa-self-hosted.md#web-backend).
 
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