feat: publish SSR under deprecated auth-helpers package names

[mandarini]

What kind of change does this PR introduce?

Feature - Package consolidation and multi-package publishing

What is the current behavior?

Currently, @supabase/ssr is only published under its own package name. Meanwhile, the deprecated @supabase/auth-helpers-* packages continue to receive thousands of weekly downloads, probably due to LLMs recommending them in code suggestions despite being deprecated for a long time.

The deprecated packages:

• @supabase/auth-helpers-nextjs (159k weekly downloads)
• @supabase/auth-helpers-react
• @supabase/auth-helpers-remix
• @supabase/auth-helpers-sveltekit

What is the new behavior?

This PR enables @supabase/ssr to be published under multiple package names simultaneously:

1. Multi-package publishing: The release workflow now publishes the same codebase under 5 different npm package names:

   • @supabase/ssr (primary package)
   • @supabase/auth-helpers-nextjs
   • @supabase/auth-helpers-react
   • @supabase/auth-helpers-remix
   • @supabase/auth-helpers-sveltekit

2. Console warnings: When imported as a deprecated auth-helpers package, users see a prominent warning.

3. Updated documentation: README clearly explains the package consolidation and lists all deprecated packages.

Additional context

Users of the old auth-helpers packages will experience breaking changes when updating, as the APIs are not backward compatible. This is intentional - as discussed internally, we want to "break it loudly" to force users to notice and migrate.

Why this approach?

• LLMs continue to recommend deprecated packages despite deprecation warnings
• Traditional deprecation methods have proven ineffective
• Publishing SSR under the old names ensures users get the maintained, working code
• Console warnings guide users to the correct package

Related: supabase/auth-helpers#811

[j4w8n]

I assume that if we're going to "break it loudly" then we're also going to shout it from the rooftops loudly one last time?? If I recall from past discussions, posts, etc, there are devs using the deprecated packages for targeted reasons - the react one specifically comes to mind but I may be mistaking it for the nextjs version.

Perhaps the "pre-LLM" devs have all migrated away by now, but if we're gonna up-and-break folks then I'd recommend treading empathetically on this one.