Add garden objects backend: polymorphic CRUD + /full (#10)

Garden objects (beds, bags, containers, in-ground, trees, paths,
structures) in one polymorphic table, following the #7 service
conventions.

- store/objects.go: scanObject + Create (RETURNING), Get, ListForGarden
  (z_index order), version-guarded Update (RETURNING, returns current row
  on conflict), Delete (plantings cascade via FK).
- store/plantings.go + plants.go: the read side /full needs now —
  ListActivePlantingsForGarden (removed_at IS NULL) and
  ListReferencedPlants (distinct plants used by active plantings). Both
  return empty until #14 adds plantings; #12/#14 extend these files.
- service/objects.go: Create/Update(partial patch)/Delete/GardenFull, all
  (ctx, actorID, ...) through requireGardenRole(editor for mutations,
  viewer for /full). finalizeObject validates kind + shape (rect/circle;
  polygon reserved), finite dims in [1cm,100m], NaN/Inf rejection, loose
  bbox-overlaps-garden placement (partial overhang OK), hex color, valid
  JSON props, name/notes caps; normalizes rotation to [0,360). Plantable
  defaults by kind, overridable.
- api/objects.go: POST /gardens/:id/objects, PATCH/DELETE /objects/:id,
  GET /gardens/:id/full ({garden,objects,plantings,plants}). props is any
  JSON value stored as text; PATCH is partial + required version, 409
  returns the current row.

Tests: service (defaults, plantable-by-kind, rotation normalize,
validation rejects incl. off-field/polygon/bad-color/bad-props, partial
patch + version conflict, cross-user ErrNotFound, delete, /full shape) and
api (CRUD + /full, 409 envelope, cross-user 404, polygon/no-kind 400,
props round-trip).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01JdQpdYYsTgtkJBxbcpAszi

internal/store/plantings.go

@@ -0,0 +1,56 @@
+package store
+
+import (
+	"context"
+	"fmt"
+
+	"gitea.stevedudenhoeffer.com/steve/pansy/internal/domain"
+)
+
+// scanPlanting reads a plantings row in table-declared column order (id,
+// object_id, plant_id, x_cm, y_cm, radius_cm, count, label, planted_at,
+// removed_at, version, created_at, updated_at) — the order SELECT pl.* yields.
+func scanPlanting(s scanner) (*domain.Planting, error) {
+	var p domain.Planting
+	if err := s.Scan(
+		&p.ID, &p.ObjectID, &p.PlantID, &p.XCM, &p.YCM, &p.RadiusCM,
+		&p.Count, &p.Label, &p.PlantedAt, &p.RemovedAt,
+		&p.Version, &p.CreatedAt, &p.UpdatedAt,
+	); err != nil {
+		return nil, err
+	}
+	return &p, nil
+}
+
+// ListActivePlantingsForGarden returns every currently-planted plop (removed_at
+// IS NULL) across all objects in a garden — the editor's one-shot load. Always a
+// non-nil slice (empty until plantings CRUD lands in #14). Plop CRUD itself is
+// #14; this is only the /full read side.
+func (d *DB) ListActivePlantingsForGarden(ctx context.Context, gardenID int64) ([]domain.Planting, error) {
+	// pl.* returns the plantings columns in table-declared order, which matches
+	// plantingColumns / scanPlanting.
+	rows, err := d.sql.QueryContext(ctx,
+		`SELECT pl.* 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,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("store: list 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
+}