feat(docker-watcher): phase 1 - project scaffold & SQLite store

Initialize Go module, directory structure, and full SQLite store layer:
- 7-table schema (projects, stages, registries, settings, instances,
  deploys, deploy_logs) with auto-migration
- CRUD operations for all entities with proper error handling
- ErrNotFound sentinel for distinguishing 404 from 500 in handlers
- WAL mode, foreign keys, busy timeout pragmas

internal/store/instances.go

@@ -0,0 +1,116 @@
+package store
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+
+	"github.com/google/uuid"
+)
+
+// CreateInstance inserts a new instance record.
+func (s *Store) CreateInstance(inst Instance) (Instance, error) {
+	inst.ID = uuid.New().String()
+	inst.CreatedAt = now()
+	inst.UpdatedAt = inst.CreatedAt
+
+	_, err := s.db.Exec(
+		`INSERT INTO instances (id, stage_id, project_id, container_id, image_tag, subdomain, npm_proxy_id, status, port, created_at, updated_at)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		inst.ID, inst.StageID, inst.ProjectID, inst.ContainerID, inst.ImageTag,
+		inst.Subdomain, inst.NpmProxyID, inst.Status, inst.Port, inst.CreatedAt, inst.UpdatedAt,
+	)
+	if err != nil {
+		return Instance{}, fmt.Errorf("insert instance: %w", err)
+	}
+	return inst, nil
+}
+
+// GetInstanceByID returns a single instance by its ID.
+func (s *Store) GetInstanceByID(id string) (Instance, error) {
+	var inst Instance
+	err := s.db.QueryRow(
+		`SELECT id, stage_id, project_id, container_id, image_tag, subdomain, npm_proxy_id, status, port, created_at, updated_at
+		 FROM instances WHERE id = ?`, id,
+	).Scan(&inst.ID, &inst.StageID, &inst.ProjectID, &inst.ContainerID, &inst.ImageTag,
+		&inst.Subdomain, &inst.NpmProxyID, &inst.Status, &inst.Port, &inst.CreatedAt, &inst.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return Instance{}, fmt.Errorf("instance %s: %w", id, ErrNotFound)
+	}
+	if err != nil {
+		return Instance{}, fmt.Errorf("query instance: %w", err)
+	}
+	return inst, nil
+}
+
+// GetInstancesByStageID returns all instances for a given stage.
+func (s *Store) GetInstancesByStageID(stageID string) ([]Instance, error) {
+	rows, err := s.db.Query(
+		`SELECT id, stage_id, project_id, container_id, image_tag, subdomain, npm_proxy_id, status, port, created_at, updated_at
+		 FROM instances WHERE stage_id = ? ORDER BY created_at DESC`, stageID,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("query instances: %w", err)
+	}
+	defer rows.Close()
+
+	var instances []Instance
+	for rows.Next() {
+		var inst Instance
+		if err := rows.Scan(&inst.ID, &inst.StageID, &inst.ProjectID, &inst.ContainerID, &inst.ImageTag,
+			&inst.Subdomain, &inst.NpmProxyID, &inst.Status, &inst.Port, &inst.CreatedAt, &inst.UpdatedAt); err != nil {
+			return nil, fmt.Errorf("scan instance: %w", err)
+		}
+		instances = append(instances, inst)
+	}
+	return instances, rows.Err()
+}
+
+// UpdateInstance updates an existing instance's mutable fields.
+func (s *Store) UpdateInstance(inst Instance) error {
+	inst.UpdatedAt = now()
+	result, err := s.db.Exec(
+		`UPDATE instances SET stage_id=?, project_id=?, container_id=?, image_tag=?, subdomain=?, npm_proxy_id=?, status=?, port=?, updated_at=?
+		 WHERE id=?`,
+		inst.StageID, inst.ProjectID, inst.ContainerID, inst.ImageTag,
+		inst.Subdomain, inst.NpmProxyID, inst.Status, inst.Port, inst.UpdatedAt, inst.ID,
+	)
+	if err != nil {
+		return fmt.Errorf("update instance: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("instance %s: %w", inst.ID, ErrNotFound)
+	}
+	return nil
+}
+
+// UpdateInstanceStatus sets only the status field on an instance.
+func (s *Store) UpdateInstanceStatus(id string, status string) error {
+	ts := now()
+	result, err := s.db.Exec(
+		`UPDATE instances SET status=?, updated_at=? WHERE id=?`,
+		status, ts, id,
+	)
+	if err != nil {
+		return fmt.Errorf("update instance status: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("instance %s: %w", id, ErrNotFound)
+	}
+	return nil
+}
+
+// DeleteInstance removes an instance by ID.
+func (s *Store) DeleteInstance(id string) error {
+	result, err := s.db.Exec(`DELETE FROM instances WHERE id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("delete instance: %w", err)
+	}
+	n, _ := result.RowsAffected()
+	if n == 0 {
+		return fmt.Errorf("instance %s: %w", id, ErrNotFound)
+	}
+	return nil
+}