## 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