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/parser.go

@@ -54,6 +54,20 @@ type rawType struct {
 	FilePath    string   `yaml:"file_path"`
 }
 
+// rawApp mirrors the YAML frontmatter of an app .md file.
+type rawApp struct {
+	Name          string   `yaml:"name"`
+	Lang          string   `yaml:"lang"`
+	Domain        string   `yaml:"domain"`
+	Description   string   `yaml:"description"`
+	Tags          []string `yaml:"tags"`
+	UsesFunctions []string `yaml:"uses_functions"`
+	UsesTypes     []string `yaml:"uses_types"`
+	Framework     string   `yaml:"framework"`
+	EntryPoint    string   `yaml:"entry_point"`
+	DirPath       string   `yaml:"dir_path"`
+}
+
 // extractFrontmatter splits a .md file into YAML frontmatter and body.
 func extractFrontmatter(data []byte) ([]byte, []byte, error) {
 	content := data
@@ -198,6 +212,51 @@ func ParseTypeMD(path string, root string) (*Type, error) {
 	return t, nil
 }
 
+// ParseAppMD parses an app .md file into an App.
+func ParseAppMD(path string, root string) (*App, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("reading %s: %w", path, err)
+	}
+
+	fm, body, err := extractFrontmatter(data)
+	if err != nil {
+		return nil, fmt.Errorf("parsing %s: %w", path, err)
+	}
+
+	var raw rawApp
+	if err := yaml.Unmarshal(fm, &raw); err != nil {
+		return nil, fmt.Errorf("parsing YAML in %s: %w", path, err)
+	}
+
+	if raw.Name == "" {
+		return nil, fmt.Errorf("%s: name is required", path)
+	}
+	if raw.Description == "" {
+		return nil, fmt.Errorf("%s: description is required", path)
+	}
+
+	sections := extractSections(body)
+
+	a := &App{
+		ID:            GenerateID(raw.Name, raw.Lang, raw.Domain),
+		Name:          raw.Name,
+		Lang:          raw.Lang,
+		Domain:        raw.Domain,
+		Description:   raw.Description,
+		Tags:          raw.Tags,
+		UsesFunctions: raw.UsesFunctions,
+		UsesTypes:     raw.UsesTypes,
+		Framework:     raw.Framework,
+		EntryPoint:    raw.EntryPoint,
+		Documentation: sections.documentation,
+		Notes:         sections.notes,
+		DirPath:       raw.DirPath,
+	}
+
+	return a, nil
+}
+
 // bodySections holds the extracted sections from a .md body.
 type bodySections struct {
 	example       string // content under ## Ejemplo