fix(test): stop the live smoke suite inheriting the loopback server list (#14583)

playwright.live.config.ts built itself with defineConfig(baseConfig, {...}),
expecting its webServer list to replace the base one. Multi-argument
defineConfig concatenates array options instead, so the live run started five
servers rather than two: the loopback OpenAI fixture, the base backend on 7860
pointed at that fixture, the base frontend on 3000, then the live backend on
7861 and a second frontend on 3000. The duplicate port 3000 with
reuseExistingServer:false failed the job before a single test ran.

The port clash was masking the real defect. Without it the suite would have
driven the base frontend, whose proxy targets the 7860 backend running against
the loopback fixture, so every "live provider" assertion would have passed
without reaching a real provider -- exactly the leak the config's comment says
it prevents.

Spreading baseConfig overrides webServer instead of appending to it. Verified
by bundling the real config: 5 webServer entries before (two on port 3000),
2 after (7861 backend, 3000 frontend), with testDir and testIgnore unchanged.