refactor: use per-source HTTP client instead of global proxy

- Remove global ProxyEnabled() logic from httpclient
- Each source now explicitly chooses client at import time:
  - flare client: for JS-rendering/cloudflare sources
  - normal httpclient: for REST API sources
- Updated 29 base sources based on Kotlin reference (network.cloudflareClient)

cmd/server/main.go

@@ -6,11 +6,9 @@ import (
 	"fmt"
 	"log"
 	"net/http"
-	"os"
 
 	"goyomi/internal/config"
 	"goyomi/internal/db"
-	"goyomi/internal/httpclient"
 	_ "goyomi/internal/registry"
 	_ "goyomi/sources/all/hentaihand"
 	_ "goyomi/sources/all/kemono"
@@ -46,16 +44,6 @@ func main() {
 	// Initialize config manager
 	config.InitConfigManager(database.Queries)
 
-	if os.Getenv("FLARESOLVERR_URL") != "" {
-		fsClient, err := httpclient.NewFlareSolverrClient()
-		if err != nil {
-			log.Printf("flaresolverr: client creation failed: %v", err)
-		} else {
-			httpclient.SetGlobalFlareSolverr(fsClient)
-			log.Printf("flaresolverr: client initialized")
-		}
-	}
-
 	mux := http.NewServeMux()
 	mux.HandleFunc("/healthz", func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintln(w, "ok")