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`

internal/route/route.go

@@ -21,6 +21,7 @@ import (
 	"github.com/yusing/godoxy/internal/docker"
 	"github.com/yusing/godoxy/internal/health/monitor"
 	"github.com/yusing/godoxy/internal/homepage"
+	iconlist "github.com/yusing/godoxy/internal/homepage/icons/list"
 	homepagecfg "github.com/yusing/godoxy/internal/homepage/types"
 	netutils "github.com/yusing/godoxy/internal/net"
 	nettypes "github.com/yusing/godoxy/internal/net/types"
@@ -850,7 +851,7 @@ func (r *Route) FinalizeHomepageConfig() {
 	hp := r.Homepage
 	refs := r.References()
 	for _, ref := range refs {
-		meta, ok := homepage.GetHomepageMeta(ref)
+		meta, ok := iconlist.GetMetadata(ref)
 		if ok {
 			if hp.Name == "" {
 				hp.Name = meta.DisplayName