p2: 120s write timeout and flags after the URL

WriteTimeout 30s was cutting digest mid-flight (queue+fetch+digest)
and tailscale then 502'd. 120s write, 90s handler deadline.
sift fetch URL --question now parses; extra positionals error.

internal/api/api.go

@@ -1,6 +1,7 @@
 package api
 
 import (
+	"context"
 	"crypto/sha256"
 	"encoding/hex"
 	"encoding/json"
@@ -24,7 +25,11 @@ import (
 	"git.wntrmute.dev/kyle/sift/internal/selfip"
 )
 
-const maxReqBody = 64 << 10
+const (
+	maxReqBody      = 64 << 10
+	writeTimeout    = 120 * time.Second
+	requestDeadline = 90 * time.Second
+)
 
 type Server struct {
 	Version string
@@ -74,7 +79,7 @@ func (s *Server) HTTPServer(addr string) *http.Server {
 		Handler:           s,
 		ReadHeaderTimeout: 5 * time.Second,
 		ReadTimeout:       15 * time.Second,
-		WriteTimeout:      30 * time.Second,
+		WriteTimeout:      writeTimeout,
 		IdleTimeout:       30 * time.Second,
 		MaxHeaderBytes:    16 << 10,
 	}
@@ -82,6 +87,12 @@ func (s *Server) HTTPServer(addr string) *http.Server {
 
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	r.Body = http.MaxBytesReader(w, r.Body, maxReqBody)
+	switch r.URL.Path {
+	case "/v1/fetch", "/v2/scrape":
+		ctx, cancel := context.WithTimeout(r.Context(), requestDeadline)
+		defer cancel()
+		r = r.WithContext(ctx)
+	}
 	s.Mux.ServeHTTP(w, r)
 }