feat(staticweb): add path prefix stripping to all filesystem providers

Add PrefixStrippingProvider interface and implement it in all providers
(EmbedFSProvider, LocalFSProvider, ZipFSProvider) to support serving
files from subdirectories at the root level.

pkg/server/staticweb/providers/zip.go

@@ -4,7 +4,9 @@ import (
 	"archive/zip"
 	"fmt"
 	"io/fs"
+	"path"
 	"path/filepath"
+	"strings"
 	"sync"
 
 	"github.com/bitechdev/ResolveSpec/pkg/server/zipfs"
@@ -12,10 +14,11 @@ import (
 
 // ZipFSProvider serves files from a zip file.
 type ZipFSProvider struct {
-	zipPath   string
-	zipReader *zip.ReadCloser
-	zipFS     *zipfs.ZipFS
-	mu        sync.RWMutex
+	zipPath     string
+	stripPrefix string
+	zipReader   *zip.ReadCloser
+	zipFS       *zipfs.ZipFS
+	mu          sync.RWMutex
 }
 
 // NewZipFSProvider creates a new ZipFSProvider for the given zip file path.
@@ -40,6 +43,9 @@ func NewZipFSProvider(zipPath string) (*ZipFSProvider, error) {
 }
 
 // Open opens the named file from the zip archive.
+// If a strip prefix is configured, it prepends the prefix to the requested path.
+// For example, with stripPrefix="/dist", requesting "/assets/style.css" will
+// open "/dist/assets/style.css" from the zip filesystem.
 func (p *ZipFSProvider) Open(name string) (fs.File, error) {
 	p.mu.RLock()
 	defer p.mu.RUnlock()
@@ -48,7 +54,21 @@ func (p *ZipFSProvider) Open(name string) (fs.File, error) {
 		return nil, fmt.Errorf("zip filesystem is closed")
 	}
 
-	return p.zipFS.Open(name)
+	// Apply prefix stripping by prepending the prefix to the requested path
+	actualPath := name
+	if p.stripPrefix != "" {
+		// Clean the paths to handle leading/trailing slashes
+		prefix := strings.Trim(p.stripPrefix, "/")
+		cleanName := strings.TrimPrefix(name, "/")
+
+		if prefix != "" {
+			actualPath = path.Join(prefix, cleanName)
+		} else {
+			actualPath = cleanName
+		}
+	}
+
+	return p.zipFS.Open(actualPath)
 }
 
 // Close releases resources held by the zip reader.
@@ -100,3 +120,19 @@ func (p *ZipFSProvider) Reload() error {
 
 	return nil
 }
+
+// WithStripPrefix sets the prefix to strip from requested paths.
+// For example, WithStripPrefix("/dist") will make files at "/dist/assets"
+// accessible via "/assets".
+func (p *ZipFSProvider) WithStripPrefix(prefix string) {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	p.stripPrefix = prefix
+}
+
+// StripPrefix returns the configured strip prefix.
+func (p *ZipFSProvider) StripPrefix() string {
+	p.mu.RLock()
+	defer p.mu.RUnlock()
+	return p.stripPrefix
+}