feat: std.http — single-worker HTTP/1.1 server core (PLAN-HTTPZ S7a)

The httpz shape, one worker, handlers inline over the std.event Loop:
nonblocking accept, per-connection state machine (reading -> writing ->
keepalive/close) with incremental parsing (request line, headers,
Content-Length body), partial-write continuation via on-demand write
interest, pipelined-request draining, and timeouts as EVICTION —
request-delivery and keepalive-idle deadlines on the monotonic clock,
checked after I/O each tick. Keep-alive is the HTTP/1.1 default;
Connection header, HTTP/1.0, or the per-connection request_count cap
turn it off. Config mirrors httpz: port/backlog/max_conn/read_buf_cap/
timeout_request_ms/timeout_keepalive_ms/request_count.

API: Server.init(cfg, handler) + tick(max_wait_ms); run() is the
forever-tick loop. tick makes the server drivable single-threaded —
examples/1633 runs a live server and its client sockets in ONE thread,
pinning: GET with keep-alive, actual connection reuse, the request cap
answering Connection: close then EOF, POST body echo, 404 routing, and
a half-header client evicted at the request deadline while a healthy
client keeps being served. Verified under sx run AND sx build.

Connection slots and read buffers are reused across connections
(httpz's min_conn/buffer-pool spirit); response buffers are allocated
per response and freed on completion. Serialization happens while
request views are valid, the served bytes are compacted, and only then
does sending start — write_more's pipelining check must see only the
remainder. The std.sx barrel carries http; .ir snapshot regen is the
usual mechanical renumbering.

S7b adds worker counts + the handler thread pool (needs C2/S6); the
epoll backend activates with the linux target (S4/S7c).

examples/expected/1309-ffi-objc-class-method-lowering.ir

@@ -1379,6 +1379,54 @@ declare i1 @expired(ptr, i64) #0
 ; Function Attrs: nounwind
 declare i64 @remaining_ms(ptr, i64) #0
 
+; Function Attrs: nounwind
+declare ptr @find_header(ptr, ptr, ptr) #0
+
+; Function Attrs: nounwind
+declare i1 @ascii_ieq(ptr, ptr, ptr) #0
+
+; Function Attrs: nounwind
+declare ptr @reason_for(ptr, i64) #0
+
+; Function Attrs: nounwind
+declare void @Server.init(ptr sret({ { { i64, i32, i64, i64, i64, i64, i64 }, { i32 }, i32, ptr, { ptr, ptr, ptr }, ptr }, i32 }), ptr, ptr, ptr) #0
+
+; Function Attrs: nounwind
+declare void @Server.close(ptr, ptr) #0
+
+; Function Attrs: nounwind
+declare i64 @Server.free_slot(ptr, ptr) #0
+
+; Function Attrs: nounwind
+declare void @Server.conn_close(ptr, ptr, i64) #0
+
+; Function Attrs: nounwind
+declare i32 @Server.tick(ptr, ptr, i64) #0
+
+; Function Attrs: nounwind
+declare void @Server.run(ptr, ptr) #0
+
+; Function Attrs: nounwind
+declare void @Server.accept_ready(ptr, ptr) #0
+
+; Function Attrs: nounwind
+declare void @Server.read_more(ptr, ptr, i64) #0
+
+; Function Attrs: nounwind
+declare void @Server.serve_buffered(ptr, ptr, i64) #0
+
+; Function Attrs: nounwind
+declare i1 @Server.try_serve_one(ptr, ptr, i64) #0
+
+; Function Attrs: nounwind
+declare void @Server.serialize_response(ptr, ptr, i64, ptr, i1) #0
+
+; Function Attrs: nounwind
+declare void @Server.write_more(ptr, ptr, i64) #0
+
+; Function Attrs: nounwind
+declare void @Server.respond_error_close(ptr, ptr, i64, i64) #0
+
 ; Function Attrs: nounwind
 declare void @BuildOptions.add_link_flag.77(i64, ptr) #0