Stream large HTTP upload bodies to disk instead of buffering

ores.http.server's generic per-connection loop (http_session::run(), projects/ores.http/api/src/net/http_session.cpp) reads every incoming request via a plain http::request_parser<http::string_body>, shared by every JSON API route and by storage_routes's PUT/GET/DELETE storage endpoints alike. That means a large binary upload (a compute engine package, tens of MB) gets fully buffered into a std::string before storage_routes::handle_put writes it to disk – correct, but not memory-efficient. The idiomatic fix is route-specific streaming: give the storage PUT/GET endpoints their own http::file_body-based read/write path that streams straight to/from disk without ever holding the whole object in RAM, mirroring what ores.storage::net::http_client::get already does client-side for downloads (streams into an http::file_body response). This needs the router/=http_request= abstraction (currently content-agnostic, body typed as std::string) to grow a way for a specific route to opt into a different body type, which is a real design change, not a one-line fix.

Discovered while fixing the ACME compute package publishing flow (task 0F768B80-184A-44C7-B725-A594A873AB4A): uploading the ~57MB vendored ORE engine package failed with a "Broken pipe" error because Beast's default body_limit for a plain parser is 1MB. The immediate fix raised http_server_options::max_body_size to 256MB so the upload is merely accepted, but that's a bound on how much can be buffered in memory per upload, not a fix for the buffering itself. At compute publishing's actual scale (a handful of admin-triggered engine publishes, not concurrent high-throughput traffic) a bounded in-memory buffer is an acceptable interim trade-off, but the buffering approach won't scale gracefully if uploads grow larger or more frequent, and streaming to disk is the more correct long-term shape for this endpoint regardless.

• projects/ores.http/api/src/net/http_session.cpp (http_session::run())
• projects/ores.http/api/include/ores.http.api/net/http_server_options.hpp (max_body_size)
• projects/ores.http/core/src/routes/storage_routes.cpp (handle_put=/=handle_get)
• projects/ores.storage/src/net/http_client.cpp (client-side file_body streaming already in place for GET)

• Task: Design and build ACME compute package publishing (client lib, shell, Qt)