build(config): regenerate config before unit tests so runs are hermetic (#4432)

test:unit / test:unit:coverage / test:watch (and thus test, test:coverage) did
not regenerate src/config/index.js first, so a run consumed whatever config the
last dev/build/e2e wrote. When that file was generated under a different NODE_ENV,
config keys that only exist under a project-specific env were absent, producing
confusing non-deterministic failures (undefined config values -> bad URLs /
ECONNREFUSED that read like broken tests).

Add pretest:unit / pretest:unit:coverage / pretest:watch hooks that run
generateConfig, respecting the current NODE_ENV. generateConfig already skips the
write when content is byte-identical, so watch mode and concurrent workers are
not disrupted.

Closes #4424

Claude-Session: https://claude.ai/code/session_01XioM62H2iEMLsr686minjn

Author: PierreBrisorgueil

package.json

@@ -29,8 +29,11 @@
     "vite:preview": "vite preview",
     "test": "npm run test:unit",
     "test:all": "npm run test:unit && npm run test:e2e",
+    "pretest:unit": "npm run generateConfig",
     "test:unit": "vitest run",
+    "pretest:unit:coverage": "npm run generateConfig",
     "test:unit:coverage": "vitest run --coverage",
+    "pretest:watch": "npm run generateConfig",
     "test:watch": "vitest",
     "test:coverage": "npm run test:unit:coverage",
     "test:e2e": "npm run generateConfig && npx playwright test --config playwright.config.js",