fix: code config values and UI settings save both ignored defaults

[FarbodGhasemi]

Ticket

N/A

Summary

Fixes two independent bugs where plugin configuration values were silently ignored.

Bug 1 — Server: plugins.ts code config values overridden by hard-coded defaults

In server/src/config/setup.ts, configSetup merged configBase.default into configRaw before
building the fallback chain. This meant the hard-coded default always appeared as a DB value and
won, so any key set in plugins.ts (e.g. allowedLevels: 5) was silently discarded.

Fix: separate the raw DB read (dbConfig) from the Zod validation object and apply the correct
priority order: DB value → code config (plugins.ts) → hard-coded default.

Bug 2 — UI: changing allowedLevels in admin settings reverts to default on save

NumberInput from @strapi/design-system delivers its parsed value via onValueChange, not
onChange. The existing onChange handler received a non-string first argument, so
isString(fieldName) returned false and setFormValueItem was never called.
formValue.allowedLevels stayed at the server's initial value while the input display (driven by
the Form component's internal state) correctly showed the user's edit — causing the stale value to
be submitted on save.

Fix: switch NumberInput to onValueChange and pass the field name explicitly to handleChange.

Additional:

• useInitialConfig: useRef guard so the form is seeded from server data only once per mount,
  preventing background refetches from overwriting in-progress edits
• useSaveConfig: invalidate the config query after a successful save
• SettingsPage: move queryClient.invalidateQueries() into useEffect (was running on every
  render)
• Test infrastructure: outDir in server/tsconfig.json + tsconfig path in jest.config.ts
  for ts-jest
• Regression test: configSetup with empty DB respects a code config allowedLevels value

Test Plan

• Set allowedLevels: 5 in config/plugins.ts with no prior DB config → server bootstraps with
  5, not 2
• Navigate to Settings, change allowedLevels to 4, click Save → PUT body contains 4; value
  persists after restart
• yarn jest → 175 passing, 2 todo, 1 pre-existing failure (CommonService › getSlug() — ESM/CJS
  issue with @sindresorhus/slugify, unrelated to this PR)