Reconsider global.json sdk.paths precedence for dotnetup init root

### Description

During `dotnetup init`, `InstallPathResolver` currently gives the first `sdk.paths` entry from the nearest `global.json` precedence over the default dotnetup install root when `--install-path` is not specified. This means running init from inside a repository can select a repository-specific SDK lookup path as the managed dotnetup hive.

This behavior became visible while adding the setup summary in #55648. That PR now identifies when the displayed install root was inferred from `global.json`, but changing the precedence is intentionally out of scope there.

### Current precedence

1. Explicit `--install-path`
2. First `sdk.paths` entry from `global.json`
3. Default dotnetup install root

### Follow-up

Decide whether first-run/init should ignore `global.json` `sdk.paths` when choosing the default managed hive, while preserving the intended behavior for explicit SDK install operations.