feat: tabla apps en registry — modelo, parser, indexer y CLI

Agrega soporte completo para indexar aplicaciones del directorio apps/.
Cada app tiene un descriptor app.md con frontmatter YAML que el indexer
recoge automaticamente. Incluye migracion 004, modelo App, ParseAppMD,
ValidateApp, store CRUD con FTS5, y soporte en fn list/search/show.
Crea descriptores app.md para docker_tui, pipeline_launcher y metabase_registry.

cmd/fn/main.go

@@ -102,7 +102,10 @@ func cmdIndex() {
 		os.Exit(1)
 	}
 
-	fmt.Printf("Indexed %d functions, %d types\n", result.Functions, result.Types)
+	// Flush WAL to main db file so external readers (e.g. Metabase) see changes.
+	db.WalCheckpoint()
+
+	fmt.Printf("Indexed %d functions, %d types, %d apps\n", result.Functions, result.Types, result.Apps)
 	for _, e := range result.ValidationErrors {
 		fmt.Fprintf(os.Stderr, "  INVALID: %s\n", e)
 	}
@@ -151,7 +154,13 @@ func cmdSearch(args []string) {
 		os.Exit(1)
 	}
 
-	if len(fns) == 0 && len(types) == 0 {
+	apps, err := db.SearchApps(query, lang, domain)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+
+	if len(fns) == 0 && len(types) == 0 && len(apps) == 0 {
 		fmt.Println("No results.")
 		return
 	}
@@ -174,6 +183,16 @@ func cmdSearch(args []string) {
 			fmt.Fprintf(w, "%s\t%s\t%s\n", t.Algebraic, t.ID, desc)
 		}
 	}
+	if len(apps) > 0 {
+		if len(fns) > 0 || len(types) > 0 {
+			fmt.Fprintln(w)
+		}
+		fmt.Fprintln(w, "APP\tID\tLANG\tDESCRIPTION")
+		for _, a := range apps {
+			desc := truncate(a.Description, 60)
+			fmt.Fprintf(w, "app\t%s\t%s\t%s\n", a.ID, a.Lang, desc)
+		}
+	}
 	w.Flush()
 }
 
@@ -212,6 +231,12 @@ func cmdList(args []string) {
 		os.Exit(1)
 	}
 
+	apps, err := db.SearchApps("", lang, domain)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "error: %v\n", err)
+		os.Exit(1)
+	}
+
 	w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
 	if len(fns) > 0 {
 		fmt.Fprintln(w, "KIND\tID\tPURITY\tVERSION\tDOMAIN")
@@ -228,7 +253,16 @@ func cmdList(args []string) {
 			fmt.Fprintf(w, "%s\t%s\t%s\t%s\n", t.Algebraic, t.ID, t.Version, t.Domain)
 		}
 	}
-	if len(fns) == 0 && len(types) == 0 {
+	if len(apps) > 0 {
+		if len(fns) > 0 || len(types) > 0 {
+			fmt.Fprintln(w)
+		}
+		fmt.Fprintln(w, "APP\tID\tLANG\tDOMAIN")
+		for _, a := range apps {
+			fmt.Fprintf(w, "app\t%s\t%s\t%s\n", a.ID, a.Lang, a.Domain)
+		}
+	}
+	if len(fns) == 0 && len(types) == 0 && len(apps) == 0 {
 		fmt.Println("Registry is empty. Run 'fn index' first.")
 	}
 	w.Flush()
@@ -258,6 +292,12 @@ func cmdShow(args []string) {
 		return
 	}
 
+	a, errA := db.GetApp(id)
+	if errA == nil {
+		printApp(a)
+		return
+	}
+
 	fmt.Fprintf(os.Stderr, "not found: %s\n", id)
 	os.Exit(1)
 }
@@ -342,6 +382,34 @@ func printType(t *registry.Type) {
 	}
 }
 
+func printApp(a *registry.App) {
+	fmt.Printf("ID:          %s\n", a.ID)
+	fmt.Printf("Name:        %s\n", a.Name)
+	fmt.Printf("Lang:        %s\n", a.Lang)
+	fmt.Printf("Domain:      %s\n", a.Domain)
+	fmt.Printf("Description: %s\n", a.Description)
+	fmt.Printf("Tags:        %s\n", strings.Join(a.Tags, ", "))
+	fmt.Printf("Dir:         %s\n", a.DirPath)
+	if a.Framework != "" {
+		fmt.Printf("Framework:   %s\n", a.Framework)
+	}
+	if a.EntryPoint != "" {
+		fmt.Printf("Entry point: %s\n", a.EntryPoint)
+	}
+	if len(a.UsesFunctions) > 0 {
+		fmt.Printf("Uses fns:    %s\n", strings.Join(a.UsesFunctions, ", "))
+	}
+	if len(a.UsesTypes) > 0 {
+		fmt.Printf("Uses types:  %s\n", strings.Join(a.UsesTypes, ", "))
+	}
+	if a.Notes != "" {
+		fmt.Printf("\nNotes:\n%s\n", a.Notes)
+	}
+	if a.Documentation != "" {
+		fmt.Printf("\nDocumentation:\n%s\n", a.Documentation)
+	}
+}
+
 // --- add ---
 
 func cmdAdd(args []string) {
@@ -367,8 +435,10 @@ func cmdAdd(args []string) {
 		templatePath = filepath.Join(r, "docs", "templates", "pipeline.md")
 	case "component":
 		templatePath = filepath.Join(r, "docs", "templates", "component.md")
+	case "app":
+		templatePath = filepath.Join(r, "docs", "templates", "app.md")
 	default:
-		fmt.Fprintf(os.Stderr, "unknown kind: %s (use function, pipeline, or component)\n", kind)
+		fmt.Fprintf(os.Stderr, "unknown kind: %s (use function, pipeline, component, or app)\n", kind)
 		os.Exit(1)
 	}