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.

registry/indexer.go

@@ -11,6 +11,7 @@ import (
 type IndexResult struct {
 	Functions        int
 	Types            int
+	Apps             int
 	ValidationErrors []string
 	Errors           []string
 }
@@ -76,6 +77,28 @@ func Index(db *DB, root string) (*IndexResult, error) {
 		})
 	}
 
+	// Parse apps from apps/*/app.md
+	var apps []*App
+	appsDir := filepath.Join(root, "apps")
+	if fi, err := os.Stat(appsDir); err == nil && fi.IsDir() {
+		entries, _ := os.ReadDir(appsDir)
+		for _, e := range entries {
+			if !e.IsDir() {
+				continue
+			}
+			appMD := filepath.Join(appsDir, e.Name(), "app.md")
+			if _, err := os.Stat(appMD); err != nil {
+				continue
+			}
+			a, err := ParseAppMD(appMD, root)
+			if err != nil {
+				result.Errors = append(result.Errors, fmt.Sprintf("parse %s: %v", appMD, err))
+				continue
+			}
+			apps = append(apps, a)
+		}
+	}
+
 	// Build known ID sets
 	knownFunctions := make(map[string]bool, len(functions))
 	for _, f := range functions {
@@ -111,6 +134,18 @@ func Index(db *DB, root string) (*IndexResult, error) {
 		result.Functions++
 	}
 
+	for _, a := range apps {
+		if verr := ValidateApp(a, knownFunctions, knownTypes); verr != nil {
+			result.ValidationErrors = append(result.ValidationErrors, verr.Error())
+			continue
+		}
+		if err := db.InsertApp(a); err != nil {
+			result.Errors = append(result.Errors, fmt.Sprintf("insert %s: %v", a.ID, err))
+			continue
+		}
+		result.Apps++
+	}
+
 	return result, nil
 }