feat(sqlite): initial stable release v0.9.0

Pure-Go CGO-free SQLite client with launcher lifecycle, write-mutex serialisation, health check, unit-of-work via context injection, and structured error mapping.

What's included:
- Executor / Tx / Client / Component interfaces using database/sql native types
- Tx.Commit() / Tx.Rollback() without ctx, matching the honest database/sql contract
- New(logger, cfg) constructor; database opened in OnInit
- Config struct with env-tag support; default Pragmas: WAL + 5s busy timeout + FK enforcement
- PRAGMA foreign_keys = ON enforced explicitly in OnInit
- writeMu sync.Mutex acquired by UnitOfWork.Do to serialise writes and prevent SQLITE_BUSY
- UnitOfWork via context injection; GetExecutor(ctx) returns active Tx or *sql.DB
- HandleError mapping SQLite extended error codes to xerrors codes (unique/primary-key → AlreadyExists, foreign-key → InvalidInput, ErrNoRows → NotFound)
- health.Checkable at LevelCritical; pure-Go modernc.org/sqlite driver (CGO_ENABLED=0 compatible)

Tested-via: todo-api POC integration
Reviewed-against: docs/adr/

errors.go

@@ -0,0 +1,38 @@
+package sqlite
+
+import (
+	"database/sql"
+	"errors"
+
+	"code.nochebuena.dev/go/xerrors"
+)
+
+// coder is the duck-type interface for SQLite extended error codes.
+// modernc.org/sqlite errors implement this interface.
+type coder interface{ Code() int }
+
+const (
+	sqliteConstraintPrimaryKey  = 1555
+	sqliteConstraintUnique      = 2067
+	sqliteConstraintForeignKey  = 787
+)
+
+// HandleError maps SQLite and database/sql errors to xerrors types.
+func HandleError(err error) error {
+	if err == nil {
+		return nil
+	}
+	if errors.Is(err, sql.ErrNoRows) {
+		return xerrors.New(xerrors.ErrNotFound, "record not found").WithError(err)
+	}
+	var ce coder
+	if errors.As(err, &ce) {
+		switch ce.Code() {
+		case sqliteConstraintUnique, sqliteConstraintPrimaryKey:
+			return xerrors.New(xerrors.ErrAlreadyExists, "record already exists").WithError(err)
+		case sqliteConstraintForeignKey:
+			return xerrors.New(xerrors.ErrInvalidInput, "data integrity violation").WithError(err)
+		}
+	}
+	return xerrors.New(xerrors.ErrInternal, "unexpected database error").WithError(err)
+}