Revert to Docker-only source paths, fix config validation, improve transcoding info

- handlers_sources.go: revert to relative paths rooted at /media (remove standalone absolute-path mode)
- settings.html: remove manual path input, restore auto-loading source tree from /media
- config.go: remove filesystem existence checks from Validate() — paths may be temporarily unavailable
- transcoder.go: always specify fps in ffmpeg args when MaxFPS is set, preserving source fps if lower than limit
- copier.go: include source codec/format and target codec/format in transcoding task message

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/handlers_sources.go

@@ -3,6 +3,7 @@ package api
 import (
 	"errors"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
 	"sort"
@@ -10,19 +11,20 @@ import (
 )
 
 func (s *Server) handleSources(w http.ResponseWriter, r *http.Request) {
-	absPath, err := normalizeSourcePathQuery(r.URL.Query().Get("path"))
+	relPath, err := normalizeSourcePath(r.URL.Query().Get("path"))
 	if err != nil {
 		jsonErr(w, http.StatusBadRequest, err.Error())
 		return
 	}
-	if absPath == "" {
-		jsonOK(w, map[string]any{"path": "", "items": []map[string]string{}})
-		return
+
+	absPath := s.deps.Config.MediaPath
+	if relPath != "" {
+		absPath = filepath.Join(absPath, relPath)
 	}
 
 	entries, err := os.ReadDir(absPath)
 	if err != nil {
-		jsonOK(w, map[string]any{"path": absPath, "items": []map[string]string{}})
+		jsonOK(w, map[string]any{"path": relPath, "items": []map[string]string{}})
 		return
 	}
 
@@ -36,10 +38,13 @@ func (s *Server) handleSources(w http.ResponseWriter, r *http.Request) {
 		if !e.IsDir() || strings.HasPrefix(e.Name(), ".") {
 			continue
 		}
-		childPath := filepath.Join(absPath, e.Name())
+		childPath := e.Name()
+		if relPath != "" {
+			childPath = filepath.Join(relPath, childPath)
+		}
 		items = append(items, item{
 			Name: e.Name(),
-			Path: childPath,
+			Path: filepath.ToSlash(childPath),
 		})
 	}
 
@@ -48,18 +53,26 @@ func (s *Server) handleSources(w http.ResponseWriter, r *http.Request) {
 	})
 
 	jsonOK(w, map[string]any{
-		"path":  absPath,
+		"path":  relPath,
 		"items": items,
 	})
 }
 
-func normalizeSourcePathQuery(raw string) (string, error) {
+func normalizeSourcePath(raw string) (string, error) {
+	raw, _ = url.QueryUnescape(raw)
 	raw = strings.TrimSpace(raw)
+	raw = filepath.ToSlash(raw)
+	raw = strings.TrimPrefix(raw, "/")
 	if raw == "" || raw == "." {
 		return "", nil
 	}
+
 	clean := filepath.Clean(raw)
-	if !filepath.IsAbs(clean) {
+	clean = filepath.ToSlash(clean)
+	if clean == "." {
+		return "", nil
+	}
+	if clean == ".." || strings.HasPrefix(clean, "../") {
 		return "", errors.New("invalid source path")
 	}
 	return clean, nil