chore(studio): improve download snippet dialog (#46242)

## What kind of change does this PR introduce?

Chore: component migration and copy update.

## What is the current behavior?

`DownloadSnippetModal` and `RenameQueryModal` use an awkward tabs-based
layout. The download action is labelled "Download" throughout, and the
NPX toggle was incorrectly labelled "NPM".

## What is the new behavior?

- Both modals are migrated to the `Dialog` component.
- The download dialog replaces the tab layout with a select (Migration /
Seed file / SQL file) and a CLI/NPX toggle.
- Action language changed from "Download" to "Export" (context menu
item, dialog title, select label) — more accurate since the user runs a
CLI command rather than triggering a browser download.
- NPM toggle label corrected to NPX; internal `npm` property key renamed
to `npx` for consistency.

| Before | After |
| --- | --- |
| <img width="1024" height="759" alt="Add Auth Hook (General) SQL Editor
Pickles Pantry Supabase-C6F22F8B-19FF-486E-8C08-915895495875"
src="https://github.com/user-attachments/assets/98637802-5e05-4431-87f8-b2e83216082a"
/> | <img width="1024" height="759" alt="Add Auth Hook (General) SQL
Editor Pickles Pantry Supabase-5B63AD0C-7CD0-4BB2-BEC8-5DBAE94963CE"
src="https://github.com/user-attachments/assets/a8f48c2f-a7e2-42fd-b52c-89a133811ad8"
/> |
| <img width="1024" height="759" alt="Add Auth Hook (General) SQL Editor
Pickles Pantry Supabase-1F28FADA-46D1-4C0A-BE96-6CFF2317FDCF"
src="https://github.com/user-attachments/assets/afb904d0-689b-4756-b0b4-8177703934e4"
/> | <img width="1024" height="759" alt="Add Auth Hook (General) SQL
Editor Pickles Pantry Supabase-652E6E8D-1CD2-4465-BC82-46EDB974CD8C"
src="https://github.com/user-attachments/assets/f1adfb6b-fba6-495f-b571-1713c3eebb4d"
/> |

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Refactor**
* Updated the SQL query export modal UI from a tabs-based interface to a
dropdown-based selection for choosing export formats.
* Revised menu and dialog labels to "Export query" for improved clarity.
  * Enhanced code block presentation in the export modal.

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---------

Co-authored-by: Gildas Garcia <1122076+djhi@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

e2e/studio/features/sql-editor.spec.ts

@@ -786,11 +786,11 @@ hello world`)
     await expect(page.getByText('result found')).toBeVisible()
     await searchBar.fill('') // clear search bar
 
-    // download as migration file
+    // export query as migration file
     await privateSnippetSection
       .getByTitle(sqlSnippetName, { exact: true })
       .click({ button: 'right' })
-    await page.getByRole('menuitem', { name: 'Download as migration file' }).click()
+    await page.getByRole('menuitem', { name: 'Export query' }).click()
     await expect(page.getByText('supabase migration new')).toBeVisible()
     await page.getByRole('button', { name: 'Close' }).click()