refactor(homepage): reorganize icons into dedicated package structure

Split the monolithic `internal/homepage` icons functionality into a structured package hierarchy:

- `internal/homepage/icons/` - Core types (URL, Key, Meta, Provider, Source, Variant)
- `internal/homepage/icons/fetch/` - Icon fetching logic (content.go, fetch.go, route.go)
- `internal/homepage/icons/list/` - Icon listing and search (list_icons.go, list_icons_test.go)

Moved icon-related code from `internal/homepage/`:
- `icon_url.go` → `icons/url.go` (+ url_test.go)
- `content.go` → `icons/fetch/content.go`
- `route.go` → `icons/fetch/route.go`
- `list_icons.go` → `icons/list/list_icons.go` (+ list_icons_test.go)

Updated all consumers to use the new package structure:
- `cmd/main.go`
- `internal/api/v1/favicon.go`
- `internal/api/v1/icons.go`
- `internal/idlewatcher/handle_http.go`
- `internal/route/route.go`

cmd/main.go

@@ -10,7 +10,7 @@ import (
 	"github.com/yusing/godoxy/internal/common"
 	"github.com/yusing/godoxy/internal/config"
 	"github.com/yusing/godoxy/internal/dnsproviders"
-	"github.com/yusing/godoxy/internal/homepage"
+	iconlist "github.com/yusing/godoxy/internal/homepage/icons/list"
 	"github.com/yusing/godoxy/internal/logging"
 	"github.com/yusing/godoxy/internal/logging/memlogger"
 	"github.com/yusing/godoxy/internal/metrics/systeminfo"
@@ -39,7 +39,7 @@ func main() {
 	log.Trace().Msg("trace enabled")
 	parallel(
 		dnsproviders.InitProviders,
-		homepage.InitIconListCache,
+		iconlist.InitCache,
 		systeminfo.Poller.Start,
 		middleware.LoadComposeFiles,
 	)