feat: add NestJS adapter

[bogdantarasenko]

Summary

Adds a community NestJS adapter under @supabase/server/adapters/nestjs, alongside the existing Hono and H3 adapters.

• withSupabase(opts) returns a class guard usable with @UseGuards() or app.useGlobalGuards(new (withSupabase(...))()). Works on both Express and Fastify platforms; HTTP/2 pseudo-headers and non-HTTP execution contexts (rpc/ws) are handled.
• @SupabaseCtx(key?, ...pipes) is a param decorator that returns the full SupabaseContext or a single field, with NestJS pipes applied to the extracted value.
• Failed auth surfaces as HttpException with { message, code }; the underlying AuthError is exposed on cause so consumers can build their own exception filters.

@nestjs/common is added as an optional peer dep (^10.0.0 || ^11.0.0), so users who don't import the adapter aren't forced to install Nest.

What's in the diff

• src/adapters/nestjs/{middleware,decorator,index}.ts — adapter source
• src/adapters/nestjs/{middleware,integration}.test.ts — unit tests for the guard/decorator plus integration tests that boot a real Nest app on Express and Fastify (covers @UseGuards, useGlobalGuards, and @SupabaseCtx with pipes)
• vitest.config.ts — uses unplugin-swc so the integration tests get emitDecoratorMetadata, which Nest's DI requires (esbuild, vitest's default transform, doesn't emit it)
• tsconfig.json — experimentalDecorators + emitDecoratorMetadata for the same reason
• tsdown.config.ts, package.json exports, jsr.json — wire the new entry point
• README.md, src/adapters/README.md, new docs/adapters/nestjs.md — documentation

Test plan

• pnpm test — unit + integration tests pass on Express and Fastify
• pnpm build — tsdown emits dist/adapters/nestjs/index.{mjs,cjs,d.mts,d.cts}
• Reviewer: confirm the optional-peer-dep approach (peerDependenciesMeta) is acceptable so non-Nest users aren't affected
• Reviewer: sanity-check the vitest.config.ts + unplugin-swc test setup; it's only needed because Nest's DI requires decorator metadata that esbuild doesn't emit