fix: preserve response cookie intent

[danceroutine]

Summary

• make TangoHeaders.setCookie() replacement-aware for helper-managed cookies with the same name, domain, and path
• add getSetCookie() so response cookies can be transferred as separate Set-Cookie lines
• preserve multiple cookie lines through TangoResponse.toWebResponse() and Express response forwarding
• add a patch changeset for the core and Express adapter behavior fix

Validation

• pnpm exec prettier --check .changeset/cookie-intent-semantics.md packages/core/src/http/TangoHeaders.ts packages/core/src/http/TangoResponse.ts packages/core/src/http/tests/TangoHeaders.test.ts packages/core/src/http/tests/TangoResponse.test.ts packages/adapters/express/src/adapter/ExpressAdapter.ts packages/adapters/express/src/adapter/tests/ExpressAdapter.test.ts
• pnpm --filter @danceroutine/tango-core test
• pnpm --filter @danceroutine/tango-adapters-express test
• pnpm --filter @danceroutine/tango-adapters-next test
• pnpm --filter @danceroutine/tango-adapters-nuxt test
• pnpm changeset status --since=origin/main
• source-level typechecks passed with --ignoreDeprecations 5.0 for core and Express prod/test configs

Typecheck note

The raw package typecheck commands currently fail before source diagnostics because this checkout uses TypeScript 5.9.3 while tsconfig.base.json has ignoreDeprecations: "6.0". The source-level checks pass when overriding that setting to 5.0.