feat(infra): sqlite_apply_versioned_migrations + dedup fn_operations + registry

Promueve patron versionado (schema_migrations + tx por archivo) al registry
como sqlite_apply_versioned_migrations_go_infra. Migra fn_operations/migrate.go
y registry/migrate.go al consumirla. ~200 LOC duplicadas eliminadas.

- functions/infra/sqlite_apply_versioned_migrations.{go,md,_test.go}: nueva,
  5/5 tests pass. Generaliza fs.FS + dir param (fn_operations usaba embed.FS
  hardcoded). Distinta de sqlite_apply_migrations_go_infra (naive split-by-`;`,
  idempotent-by-error) — esta hace tracking explicito + transactions.
- fn_operations/migrate.go: 111 LOC -> 17. Wrapper sobre infra.ApplyVersionedMigrations.
- registry/migrate.go: idem. Mismo patron copy-paste, ahora unificado.

Smoke: ./fn ops init crea operations.db con schema_migrations poblada.
fn_operations + registry tests: PASS. fn index registra nueva fn (1091 total).

functions/infra/sqlite_apply_versioned_migrations.go

@@ -0,0 +1,127 @@
+package infra
+
+import (
+	"database/sql"
+	"fmt"
+	"io/fs"
+	"path"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const createSchemaMigrationsTable = `
+CREATE TABLE IF NOT EXISTS schema_migrations (
+	version    INTEGER PRIMARY KEY,
+	name       TEXT    NOT NULL,
+	applied_at TEXT    NOT NULL
+);`
+
+// ApplyVersionedMigrations applies pending SQLite migrations from fsys, tracking
+// applied versions in a schema_migrations table. Each migration runs in its
+// own transaction; on error the tx is rolled back and the function returns.
+//
+// Migration filenames must be NNN_name.sql (e.g. 001_init.sql,
+// 002_add_users.sql). The numeric prefix is the version. Files without a
+// numeric prefix or with non-.sql extensions are skipped.
+//
+// dir is the directory inside fsys containing the migrations (e.g.
+// "migrations"). Idempotent: migrations whose version <= current are skipped.
+func ApplyVersionedMigrations(conn *sql.DB, fsys fs.FS, dir string) error {
+	if _, err := conn.Exec(createSchemaMigrationsTable); err != nil {
+		return fmt.Errorf("apply_versioned_migrations: create schema_migrations: %w", err)
+	}
+
+	current, err := versionedMigrationsCurrentVersion(conn)
+	if err != nil {
+		return err
+	}
+
+	files, err := versionedMigrationsList(fsys, dir)
+	if err != nil {
+		return err
+	}
+
+	for _, mf := range files {
+		if mf.version <= current {
+			continue
+		}
+
+		content, err := fs.ReadFile(fsys, path.Join(dir, mf.filename))
+		if err != nil {
+			return fmt.Errorf("apply_versioned_migrations: read %s: %w", mf.filename, err)
+		}
+
+		tx, err := conn.Begin()
+		if err != nil {
+			return fmt.Errorf("apply_versioned_migrations: begin tx for %s: %w", mf.filename, err)
+		}
+
+		if _, err := tx.Exec(string(content)); err != nil {
+			tx.Rollback() //nolint:errcheck
+			return fmt.Errorf("apply_versioned_migrations: exec %s: %w", mf.filename, err)
+		}
+
+		if _, err := tx.Exec(
+			"INSERT INTO schema_migrations (version, name, applied_at) VALUES (?, ?, ?)",
+			mf.version, mf.filename, time.Now().UTC().Format(time.RFC3339),
+		); err != nil {
+			tx.Rollback() //nolint:errcheck
+			return fmt.Errorf("apply_versioned_migrations: record %s: %w", mf.filename, err)
+		}
+
+		if err := tx.Commit(); err != nil {
+			return fmt.Errorf("apply_versioned_migrations: commit %s: %w", mf.filename, err)
+		}
+	}
+
+	return nil
+}
+
+// versionedMigrationsCurrentVersion returns MAX(version) from schema_migrations,
+// or 0 if the table is empty.
+func versionedMigrationsCurrentVersion(conn *sql.DB) (int, error) {
+	var v int
+	err := conn.QueryRow("SELECT COALESCE(MAX(version), 0) FROM schema_migrations").Scan(&v)
+	if err != nil {
+		return 0, fmt.Errorf("apply_versioned_migrations: read current version: %w", err)
+	}
+	return v, nil
+}
+
+type versionedMigrationFile struct {
+	version  int
+	filename string
+}
+
+// versionedMigrationsList reads dir from fsys and returns .sql files with a
+// numeric NNN_ prefix, sorted by version ascending.
+func versionedMigrationsList(fsys fs.FS, dir string) ([]versionedMigrationFile, error) {
+	entries, err := fs.ReadDir(fsys, dir)
+	if err != nil {
+		return nil, fmt.Errorf("apply_versioned_migrations: read dir %q: %w", dir, err)
+	}
+
+	var files []versionedMigrationFile
+	for _, e := range entries {
+		if e.IsDir() || !strings.HasSuffix(e.Name(), ".sql") {
+			continue
+		}
+		parts := strings.SplitN(e.Name(), "_", 2)
+		if len(parts) < 2 {
+			continue
+		}
+		v, err := strconv.Atoi(parts[0])
+		if err != nil {
+			continue
+		}
+		files = append(files, versionedMigrationFile{version: v, filename: e.Name()})
+	}
+
+	sort.Slice(files, func(i, j int) bool {
+		return files[i].version < files[j].version
+	})
+
+	return files, nil
+}