Bun parity: preserve final response URLs after redirects

Port js/web/fetch/fetch-url-after-redirect.test.ts from the copied Bun corpus.

Required behavior:

• expose the originating IncomingMessage as ServerResponse.req
• honor the full writeHead(status, statusMessage, headers) overload
• follow the complete redirect chain and preserve the final target in Response.url
• decode raw non-ASCII Location header bytes as UTF-8 before URL serialization to avoid double encoding
• provide structured Node HTTP response operation, phase, method, URL, cause, and composed stack context for response failures
• add a permanent focused regression and advance corpus position 4147 with zero failures or unsupported tests

Tracked under #66.

Completed in 51d2f9d and pushed directly to main.

Implemented:

• ServerResponse.req linked to the originating IncomingMessage
• full writeHead(status, statusMessage, headers) overload support
• complete redirect chain final URL preservation
• raw byte-valued Location header decoding through strict UTF-8 before URL serialization, avoiding double encoding
• NodeHTTPServerResponseError with ERR_HTTP_SERVER_RESPONSE, operation, phase, method, URL, cause, and composed stack
• permanent focused regression for both upstream cases

Validation:

• indexed Bun corpus position 4147: 2 passed, 0 failed, 0 todo, 0 unsupported
• focused final redirect URL regression: passed
• zig build --cache-dir /private/tmp/home-zig-abi-cache: passed