refactor: usar sqlite_apply_migrations_go_infra del registry

Sustituye applyMigrations + splitSQLStatements + isIdempotentError locales
por infra.ApplyMigrations del registry. ~55 LOC eliminadas.

- store.go: import fn-registry/functions/infra, llama infra.ApplyMigrations
- go.mod: declara dep fn-registry con replace local
- app.md: declara sqlite_apply_migrations_go_infra en uses_functions

Sin cambio funcional (mismo parser naive de `;`, mismas reglas idempotentes).
Bug fixes futuros se aplicaran automaticamente al consumir registry.

app.md

@@ -4,7 +4,8 @@ lang: go
 domain: infra
 description: "Servidor de deploy continuo para apps del registry. Recibe webhooks de Gitea, gestiona targets de deploy en operations.db y orquesta deploys a VPS remotos via SSH. Soporta tres estrategias: systemd, systemd-remote y docker-compose."
 tags: [service, deploy, ci, cd, webhook, gitea, ssh, vps, docker-compose, systemd]
-uses_functions: []
+uses_functions:
+  - sqlite_apply_migrations_go_infra
 uses_types: []
 framework: "net/http"
 entry_point: "main.go"