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/migrations/004_apps.sql

@@ -0,0 +1,48 @@
+-- Apps table: applications that consume functions/types from the registry.
+
+CREATE TABLE IF NOT EXISTS apps (
+    id               TEXT PRIMARY KEY,
+    name             TEXT NOT NULL,
+    lang             TEXT NOT NULL,
+    domain           TEXT NOT NULL,
+    description      TEXT NOT NULL,
+    tags             TEXT NOT NULL DEFAULT '[]',
+    uses_functions   TEXT NOT NULL DEFAULT '[]',
+    uses_types       TEXT NOT NULL DEFAULT '[]',
+    framework        TEXT NOT NULL DEFAULT '',
+    entry_point      TEXT NOT NULL DEFAULT '',
+    documentation    TEXT NOT NULL DEFAULT '',
+    notes            TEXT NOT NULL DEFAULT '',
+    dir_path         TEXT NOT NULL DEFAULT '',
+    created_at       TEXT NOT NULL,
+    updated_at       TEXT NOT NULL
+);
+
+CREATE VIRTUAL TABLE IF NOT EXISTS apps_fts USING fts5(
+    id,
+    name,
+    description,
+    tags,
+    domain,
+    documentation,
+    notes,
+    content='apps',
+    content_rowid='rowid'
+);
+
+CREATE TRIGGER IF NOT EXISTS apps_ai AFTER INSERT ON apps BEGIN
+    INSERT INTO apps_fts(rowid, id, name, description, tags, domain, documentation, notes)
+    VALUES (new.rowid, new.id, new.name, new.description, new.tags, new.domain, new.documentation, new.notes);
+END;
+
+CREATE TRIGGER IF NOT EXISTS apps_ad AFTER DELETE ON apps BEGIN
+    INSERT INTO apps_fts(apps_fts, rowid, id, name, description, tags, domain, documentation, notes)
+    VALUES ('delete', old.rowid, old.id, old.name, old.description, old.tags, old.domain, old.documentation, old.notes);
+END;
+
+CREATE TRIGGER IF NOT EXISTS apps_au AFTER UPDATE ON apps BEGIN
+    INSERT INTO apps_fts(apps_fts, rowid, id, name, description, tags, domain, documentation, notes)
+    VALUES ('delete', old.rowid, old.id, old.name, old.description, old.tags, old.domain, old.documentation, old.notes);
+    INSERT INTO apps_fts(rowid, id, name, description, tags, domain, documentation, notes)
+    VALUES (new.rowid, new.id, new.name, new.description, new.tags, new.domain, new.documentation, new.notes);
+END;