feat: add TanStack Start adapter

[wobsoriano]

What kind of change does this PR introduce?

Feature

What is the current behavior?

Developers building apps with TanStack Start have to wire up Supabase auth manually with the core primitives in every server function and server route.

What is the new behavior?

Adds @supabase/server/adapters/tanstack-start, a first-class request middleware adapter for TanStack Start. It exposes withSupabase as a TanStack Start request middleware, so the same middleware works for both server functions and server routes; in either, the SupabaseContext is available (and typed) as context.supabaseContext in the handler.

It is framework-agnostic: it imports from @tanstack/start-client-core, which every @tanstack/{react,solid,vue}-start package re-exports. So one adapter covers React, Solid, and Vue Start.

Usage in a server function:

import { createServerFn } from '@tanstack/react-start'
import { withSupabase } from '@supabase/server/adapters/tanstack-start'

export const getTodos = createServerFn()
  .middleware([withSupabase({ auth: 'user' })])
  .handler(async ({ context }) => {
    const { data } = await context.supabaseContext.supabase
      .from('todos')
      .select()
    return data
  })

Usage in a server route (src/routes/api/todos.ts):

import { createFileRoute } from '@tanstack/react-router'
import { withSupabase } from '@supabase/server/adapters/tanstack-start'

export const Route = createFileRoute('/api/todos')({
  server: {
    middleware: [withSupabase({ auth: 'user' })],
    handlers: {
      GET: async ({ context }) => {
        const { data } = await context.supabaseContext.supabase
          .from('todos')
          .select()
        return Response.json(data)
      },
    },
  },
})

Per-route auth, since middleware is attached per server function or per route:

// User-authenticated
export const listTodos = createServerFn()
  .middleware([withSupabase({ auth: 'user' })])
  .handler(async ({ context }) => context.supabaseContext.userClaims)

// Secret-key-protected (e.g. a trusted server-to-server call)
export const syncAuditLog = createServerFn({ method: 'POST' })
  .middleware([withSupabase({ auth: 'secret' })])
  .handler(async ({ context }) =>
    context.supabaseContext.supabaseAdmin
      .from('audit_log')
      .insert({ action: 'sync' }),
  )

Additional context

• Test coverage mirrors the Hono and H3 adapter tests.
• Docs and package metadata were updated to include TanStack Start in the adapter tables, exports, jsr.json, and build entry.