doc(skills): pgmigrate clarificaton

skills/use-sql-migrate-postgres/SKILL.md

@@ -19,19 +19,54 @@ PG_URL='postgres://user:pass@localhost:5432/mydb?sslmode=disable'
 
 ## Go library
 
+Use `sqlmigrate.Collect(fsys, subpath)` first to parse the embedded files.
+
+**`//go:embed` constraint:** embed cannot traverse `..`, so the embed directive must live in a package that is at or above the `sql/migrations/` directory. Pass `fs.FS` down to migration helpers rather than embedding inside them.
+
 ```go
 import (
+    "embed"
+    "io/fs"
+
     "github.com/jackc/pgx/v5"
     "github.com/therootcompany/golib/database/sqlmigrate"
     "github.com/therootcompany/golib/database/sqlmigrate/pgmigrate"
 )
 
+//go:embed sql/migrations
+var migrationsFS embed.FS
+
+func runMigrations(ctx context.Context, pgURL string) error {
+    scripts, err := sqlmigrate.Collect(migrationsFS, "sql/migrations")
+    if err != nil {
+        return err
+    }
+
     // MUST: use pgx.Connect (single conn), not pgxpool.New
     conn, err := pgx.Connect(ctx, pgURL)
+    if err != nil {
+        return err
+    }
     defer func() { _ = conn.Close(ctx) }()
 
     runner := pgmigrate.New(conn)
-applied, err := sqlmigrate.Latest(ctx, runner, scripts)
+    _, err = sqlmigrate.Latest(ctx, runner, scripts)
+    return err
+}
+```
+
+### Key types
+
+```go
+// sqlmigrate.Script — one migration pair (up + down SQL + name + ID)
+// sqlmigrate.Migration — name + ID only (returned by Applied, Latest, etc.)
+// sqlmigrate.Status — Applied []Migration + Pending []Migration
+
+scripts, err := sqlmigrate.Collect(fsys, subpath)  // parse fs.FS → []Script
+applied, err := sqlmigrate.Latest(ctx, r, scripts)  // apply all pending → []Migration
+applied, err := sqlmigrate.Up(ctx, r, scripts, n)   // apply n migrations
+rolled,  err := sqlmigrate.Down(ctx, r, scripts, n) // roll back n migrations
+status,  err := sqlmigrate.GetStatus(ctx, r, scripts)
 ```
 
 ## Schema multi-tenancy
@@ -61,4 +96,4 @@ runner := pgmigrate.New(conn)
 - `ON CONFLICT DO NOTHING` for idempotent seeds
 - String concatenation: `id || CHR(9) || name` (used by sync query)
 - Timestamps: `TIMESTAMP DEFAULT CURRENT_TIMESTAMP`
-- Error code 42P01 = table doesn't exist (handled automatically by pgmigrate)
+- Error code 42P01 = table doesn't exist (handled automatically by pgmigrate for initial migration)