## Summary
Continues the SQLEditor decomposition. Pulls four cohesive concerns out
of the `SQLEditorContent` composition root into co-located `use*` hooks.
## New hooks
- `useSnippetIdentity` — derives `id` / `generatedNewSnippetName` /
`isLoading` from the URL + snippet store (keeps the `[urlId]` memo dep
verbatim).
- `useEditorMount` — the editor `onMount` (scroll restore/track) + the
mount counter that lets a pre-mount diff request re-run.
- `usePrettifyQuery` — formats the editor SQL in place and writes it
back to the store.
- `useSnippetTitleGenerator` — the title-generation mutation +
`setAiTitle`.
