chore: lift wrangler to 4.125.0 and drop the miniflare/undici resolution (#24794)

## Summary

Parent bump instead of a pin. `wrangler ^4.0.0` (twenty-website) now
resolves 4.125.0, whose `miniflare@5.20260820.0-alpha` pins
`undici@7.29.0` on its own. The `miniflare/undici: ^7.29.0` resolution
therefore no longer forces anything and is dropped (27 to 26). The
`//resolutions` doc's undici entry is reworded to cover
`@module-federation/dts-plugin/undici` alone and records why the
miniflare sibling went.

No `package.json` range change: `yarn up -R wrangler` lifted within the
existing caret.

## Lockfile

| Package | Before | After |
|---|---|---|
| wrangler | 4.118.0 | 4.125.0 |
| miniflare | 5.20260730.0-alpha | 5.20260820.0-alpha |
| workerd (+5 platform binaries) | 1.20260730.1 | 1.20260820.1 |

Nothing else moves. undici stays at 7.29.0 for every 7.x consumer (the
former `undici@npm:7.28.0` descriptor merges into it) and 6.28.0 for
node-gyp.

## Verification

- `miniflare` block in `yarn.lock` now declares `undici: "npm:7.29.0"`
with no resolution in play.
- `yarn install --immutable` passes.
- `wrangler --version` reports 4.125.0; twenty-website only uses
wrangler as a CLI (`cf-typegen`, deploy), nothing imports it.
- wrangler 4.119 to 4.125 release notes carry no breaking changes (only
`@cloudflare/vitest-pool-workers` compat-flag handling, which this repo
does not use).