fix: drop eight mintlify resolutions obsoleted by the mintlify lift (#24715)

## Summary

**Rebased on #24698**, which lifted mintlify to 4.2.816. That lift is
already on main, so this PR narrows to what remains: the refreshed
`@mintlify/*` chain now carries every fix we were forcing onto it by
hand, but the **eight pins were left in place**. This drops them - **40
-> 32 resolutions** - each verified against the parent's own dependency
edge in the lockfile.

| Dropped | Parent's own edge on main |
|---|---|
|
`@mintlify/{cli,common,prebuild,previewing,scraping,validation}/js-yaml`
(6) | every package pins `js-yaml 4.3.1` itself |
| `@mintlify/previewing/tar` | previewing pins `tar 7.5.21` itself |
| `@mintlify/common/postcss` | common pins `postcss 8.5.23` itself |

Unchanged: `next/postcss` (next still pins 8.4.31), `express/qs`
(previewing still pins express 4.22.0), the `front-matter/js-yaml` pin +
patch (deliberate, documented), and all four pins #24698 added.
`//resolutions` records each drop with its reason.

## Verification

- **The lockfile changes by exactly two lines**: the orphaned `tar
^7.5.16` descriptor - which only our pin ever produced - gives way to
previewing's own `7.5.21` descriptor. No resolved version moves: js-yaml
3.15.1 / 4.3.1 / 5.2.2, tar 7.5.21 / 7.5.22, postcss 8.5.23 only, axios
1.18.0 / 1.18.1 / 1.19.0, adm-zip 0.6.0 only, mintlify 4.2.816.
- `yarn install --immutable` passes on the rebased tree.
- Earlier pre-rebase verification (`nx lint twenty-docs`, patched
front-matter parsing docs front-matter on the forced js-yaml 4.3.1,
`mintlify validate`) was run against the same chain versions and holds;
validate's only output is a pre-existing Crowdin artifact in
`l/ar/user-guide/getting-started/capabilities/implementation-services.mdx`
(`cols={2}` machine-translated to `cols={٢}`, from the i18n bot's
#23455) - worth a fix on the i18n side, unrelated here.