fix(e2e): let web-e2e:e2e run outside CI

Without CI, every web-e2e webServer has reuseExistingServer, so
@nx/playwright infers a continuous web:serve dependency for the
`pnpm nx run web:serve` entry. The mocks and the web backend launch as
plain node processes with env, which no Nx task covers, so the plugin
also marks the target non-parallel. Nx refuses a non-parallel task with
continuous dependencies, and `nx run web-e2e:e2e` failed before running
anything; CI passed only because CI=1 disables reuse and with it the
inferred dependency.

Give web-e2e:e2e an empty dependsOn so Playwright starts every server,
as it already does in CI. The Angular dev-server runs inside the Nx
process, so Playwright's process-group kill still stops it. Turn off
the plugin's readiness gate, which no target consumes any more.

Add `pnpm run e2e:task-graphs:validate`: it builds every Playwright
target's task graph with Nx's own validation, with CI unset and set,
and runs in the unit-and-typecheck job.

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

.github/workflows/ci.yml

@@ -375,6 +375,12 @@ jobs:
             - name: Validate stylesheet Nx inputs
               run: pnpm run styles:inputs:validate
 
+            # Nx rejects a non-parallel task with continuous dependencies, and
+            # the Playwright plugin infers serve dependencies only when CI is
+            # unset, so this checks both the local and the CI inference.
+            - name: Validate Playwright task graphs
+              run: pnpm run e2e:task-graphs:validate
+
             - name: Typecheck web and Electron entry points
               run: pnpm run typecheck:ci