Copy a garden (deep duplicate) from the gardens list

Adds POST /gardens/:id/copy: duplicates a garden the actor owns, along
with its objects and their currently-planted plops, into a new garden
owned by the actor. A blank name derives "<source> (copy)".

Deliberately not carried over:
  * public_token — the share link is a capability granted to the
    original; a copy must not silently inherit a live public URL
  * garden_shares — a copy is private to whoever made it
  * removed plantings — the copy is a fresh layout, not a history

Owner-only for now: a copy's plops keep pointing at the SOURCE's
plant_ids, so letting a viewer copy someone else's garden would hand
them plants outside their catalog and pin the original owner's plants
against deletion (plantings.plant_id is ON DELETE RESTRICT). Copying a
shared garden needs a plant-cloning policy first.

The whole copy runs in one transaction, so a failure part-way leaves no
half-populated garden. The object/planting list scans are factored into
queryObjects/queryPlantings so the same code serves a plain read and a
read inside that transaction.

UI: a Copy action on the owner's garden card opens a modal prefilled
with the derived name, then lands in the new garden.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

internal/store/plantings.go

@@ -30,13 +30,19 @@ func scanPlanting(s scanner) (*domain.Planting, error) {
 // IS NULL) across all objects in a garden — the editor's one-shot load. Always a
 // non-nil slice. The service fills each row's DerivedCount; this is the raw read.
 func (d *DB) ListActivePlantingsForGarden(ctx context.Context, gardenID int64) ([]domain.Planting, error) {
-	rows, err := d.sql.QueryContext(ctx,
+	return queryPlantings(ctx, d.sql,
 		`SELECT `+qualifyColumns("pl", plantingColumns)+` FROM plantings pl
 		   JOIN garden_objects o ON o.id = pl.object_id
 		  WHERE o.garden_id = ? AND pl.removed_at IS NULL
 		  ORDER BY pl.id`,
-		gardenID,
-	)
+		gardenID)
+}
+
+// queryPlantings runs a planting query and scans every row. Like queryObjects it
+// drains and closes the cursor before returning, so a transaction caller may
+// write afterwards. Always a non-nil slice.
+func queryPlantings(ctx context.Context, q queryer, query string, args ...any) ([]domain.Planting, error) {
+	rows, err := q.QueryContext(ctx, query, args...)
 	if err != nil {
 		return nil, fmt.Errorf("store: list plantings: %w", err)
 	}
@@ -60,27 +66,9 @@ func (d *DB) ListActivePlantingsForGarden(ctx context.Context, gardenID int64) (
 // (removed_at IS NULL). Always a non-nil slice. Used by FillRegion to avoid
 // stacking new plops inside existing ones.
 func (d *DB) ListActivePlantingsForObject(ctx context.Context, objectID int64) ([]domain.Planting, error) {
-	rows, err := d.sql.QueryContext(ctx,
+	return queryPlantings(ctx, d.sql,
 		`SELECT `+plantingColumns+` FROM plantings WHERE object_id = ? AND removed_at IS NULL ORDER BY id`,
-		objectID,
-	)
-	if err != nil {
-		return nil, fmt.Errorf("store: list object plantings: %w", err)
-	}
-	defer rows.Close()
-
-	plantings := []domain.Planting{}
-	for rows.Next() {
-		p, err := scanPlanting(rows)
-		if err != nil {
-			return nil, fmt.Errorf("store: scan planting: %w", err)
-		}
-		plantings = append(plantings, *p)
-	}
-	if err := rows.Err(); err != nil {
-		return nil, fmt.Errorf("store: iterate plantings: %w", err)
-	}
-	return plantings, nil
+		objectID)
 }
 
 // ClearObjectPlantings soft-removes every active plop in an object in one UPDATE