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)

sources/base/fuzzydoodle/fuzzydoodle.go

@@ -10,7 +10,7 @@ import (
 
 	"github.com/PuerkitoBio/goquery"
 
-	"goyomi/internal/httpclient"
+	"goyomi/internal/httpclient/flare"
 	"goyomi/internal/source"
 	"goyomi/sources/base/util"
 )
@@ -23,12 +23,12 @@ type Config struct {
 
 type Source struct {
 	cfg    Config
-	client *httpclient.Client
+	client *flare.Client
 	id     int64
 }
 
 func New(cfg Config) *Source {
-	c := httpclient.NewClient(httpclient.WithRateLimit(1, 2))
+	c := flare.NewClient(flare.WithRateLimit(1, 2))
 	return &Source{cfg: cfg, client: c, id: source.GenerateSourceID(cfg.Name, cfg.Lang)}
 }