fix: use cross-spawn to resolve DEP0190 in dataconnect init

[fredzqm]

Fixes a Node.js DEP0190 DeprecationWarning that occurs when running firebase init dataconnect while creating an app template.

The warning (Passing args to a child process with shell option true can lead to security vulnerabilities) was triggered because child_process.spawn was used with the shell: true option to ensure commands like npm and npx ran correctly on all platforms.

This fix updates src/init/features/dataconnect/create_app.ts to use cross-spawn instead, which properly escapes arguments and handles cross-platform execution (especially on Windows) without needing the unsafe shell: true option.

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PR created automatically by Jules for task 8312636168148387415 started by @fredzqm

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[gemini-code-assist]

Code Review

This pull request replaces the native child_process spawn with cross-spawn and removes the shell: true option when executing commands. The reviewer points out that removing shell: true prevents manual shell-quoting of arguments from being stripped, which will cause issues in createNextApp where nested double quotes are used for the import alias. The reviewer suggests updating createNextApp to remove the nested double quotes.

[gemini-code-assist]

With the removal of shell: true, arguments are no longer evaluated by a shell. This means any manual shell-quoting of arguments in the calling functions is no longer stripped and will be passed literally to the spawned process.

Specifically, in createNextApp (around line 23), the import alias argument is defined as '"@/*"'. Because shell: true is removed, the literal double quotes will be passed to create-next-app, resulting in an invalid import alias configuration in the generated Next.js app.

Please update createNextApp to remove the nested double quotes:

    "--import-alias",
    "@/*",