Add plantings backend: plop CRUD, derived counts, removed_at (#14)

- domain: Planting gains a computed (non-persisted) DerivedCount field.
- store/plantings.go: Get/Create/Update (version-guarded)/Delete alongside the
  existing /full read helper.
- service/plantings.go: place/move/resize/soft-remove a plop; editor role on the
  object's garden; object must be plantable; plant_id must be visible to the
  actor (built-in or own) else ErrInvalidInput; center must sit within the
  object's unrotated local bounds (radius may overhang); planted_at defaults to
  today. derivedCount = max(1, round(π·r²/spacing²)) — one unit-tested helper,
  reused by /full (via a spacing map, no N+1) and single responses.
- api: POST /objects/:id/plantings, PATCH/DELETE /plantings/:id; nullable
  count/label/plantedAt/removedAt use RawMessage so null (clear) is distinct
  from absent (unchanged). removedAt is the soft-remove / "clear bed" seam.
- /full now enriches each active plop with its derivedCount.

Service tests: formula edge cases (tiny radius → 1), defaults + derived, count
override, move/resize + clear override, non-plantable rejection, foreign/unknown
plant rejection, bounds, soft-remove leaves /full, version conflict, cross-user
masking, delete. Plus an API-level create/patch/full/delete flow.

GOWORK=off go build/vet/test ./internal/... green.

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

internal/store/plantings.go

@@ -2,6 +2,8 @@ package store
 
 import (
 	"context"
+	"database/sql"
+	"errors"
 	"fmt"
 
 	"gitea.stevedudenhoeffer.com/steve/pansy/internal/domain"
@@ -54,3 +56,78 @@ func (d *DB) ListActivePlantingsForGarden(ctx context.Context, gardenID int64) (
 	}
 	return plantings, nil
 }
+
+// GetPlanting returns the planting with the given id, or domain.ErrNotFound.
+func (d *DB) GetPlanting(ctx context.Context, id int64) (*domain.Planting, error) {
+	p, err := scanPlanting(d.sql.QueryRowContext(ctx,
+		`SELECT `+plantingColumns+` FROM plantings WHERE id = ?`, id))
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, domain.ErrNotFound
+	}
+	if err != nil {
+		return nil, fmt.Errorf("store: get planting: %w", err)
+	}
+	return p, nil
+}
+
+// CreatePlanting inserts a plop (fields already validated by the service) and
+// returns the stored row. removed_at is always NULL on create — a new plop is
+// active; "clear bed" sets removed_at later via UpdatePlanting.
+func (d *DB) CreatePlanting(ctx context.Context, p *domain.Planting) (*domain.Planting, error) {
+	created, err := scanPlanting(d.sql.QueryRowContext(ctx,
+		`INSERT INTO plantings (object_id, plant_id, x_cm, y_cm, radius_cm, count, label, planted_at)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?)
+		 RETURNING `+plantingColumns,
+		p.ObjectID, p.PlantID, p.XCM, p.YCM, p.RadiusCM, p.Count, p.Label, p.PlantedAt,
+	))
+	if err != nil {
+		return nil, fmt.Errorf("store: insert planting: %w", err)
+	}
+	return created, nil
+}
+
+// UpdatePlanting applies a version-guarded update of all mutable columns (the
+// service merges partial patches first). Returns the updated row, or
+// (current row, ErrVersionConflict) / ErrNotFound — the same contract as the
+// other mutable resources.
+func (d *DB) UpdatePlanting(ctx context.Context, p *domain.Planting) (*domain.Planting, error) {
+	updated, err := scanPlanting(d.sql.QueryRowContext(ctx,
+		`UPDATE plantings
+		    SET plant_id = ?, x_cm = ?, y_cm = ?, radius_cm = ?, count = ?, label = ?,
+		        planted_at = ?, removed_at = ?,
+		        version = version + 1,
+		        updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
+		  WHERE id = ? AND version = ?
+		  RETURNING `+plantingColumns,
+		p.PlantID, p.XCM, p.YCM, p.RadiusCM, p.Count, p.Label, p.PlantedAt, p.RemovedAt,
+		p.ID, p.Version,
+	))
+	if errors.Is(err, sql.ErrNoRows) {
+		current, gerr := d.GetPlanting(ctx, p.ID)
+		if gerr != nil {
+			return nil, gerr
+		}
+		return current, domain.ErrVersionConflict
+	}
+	if err != nil {
+		return nil, fmt.Errorf("store: update planting: %w", err)
+	}
+	return updated, nil
+}
+
+// DeletePlanting hard-deletes a plop (for mistakes; "removed/harvested" flows set
+// removed_at instead). Returns domain.ErrNotFound if no row was deleted.
+func (d *DB) DeletePlanting(ctx context.Context, id int64) error {
+	res, err := d.sql.ExecContext(ctx, `DELETE FROM plantings WHERE id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("store: delete planting: %w", err)
+	}
+	n, err := res.RowsAffected()
+	if err != nil {
+		return fmt.Errorf("store: planting delete rows: %w", err)
+	}
+	if n == 0 {
+		return domain.ErrNotFound
+	}
+	return nil
+}