Extends the plants store (which had only the /full read side) with full
catalog CRUD, adds a service layer with visibility/immutability rules, REST
endpoints, and a seed migration of ~32 built-ins.

- 0003_seed_plants.sql: 32 built-in plants (owner_id NULL, read-only), seeded
  once by the version-tracked migration runner.
- store: ListPlantsForActor (built-ins + own), Get/Create/Update/Delete +
  CountPlantingsForPlant; isForeignKeyViolation backstop for the RESTRICT FK.
- service: built-ins are read-only (ErrForbidden); another user's plants are
  invisible (ErrNotFound); delete of a referenced plant → ErrPlantInUse (409);
  validation mirrors the schema (category enum, spacing>0, hex color, icon).
- api: GET,POST /plants and PATCH,DELETE /plants/:id with the version guard.
- Made the migration-count store tests derive their expectation from the files
  so future migrations don't break them.

Service + API tests cover visibility, built-in immutability, validation,
version conflict, and delete-in-use.

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

@@ -0,0 +60,4 @@
+// parseNullableInt decodes a JSON number|null field into (value, present).
+// Absent → (nil, false); null → (nil, true); 42 → (&42, true). A non-integer
+// value is an error.
+func parseNullableInt(raw json.RawMessage) (value *int, present bool, err error) {

@@ -0,0 +9,4 @@
+	"gitea.stevedudenhoeffer.com/steve/pansy/internal/domain"
+)
+
+func intPtr(n int) *int { return &n }

@@ -56,0 +59,4 @@
+// maxPlantsListed caps ListPlantsForActor as a defensive backstop. The seeded
+// built-ins (~30) plus a user's own catalog stay tiny at household scale, so this
+// is never hit; pagination is post-v1 if ever needed.
+const maxPlantsListed = 5000

@@ -56,0 +167,4 @@
+// DeletePlant removes a plant. Returns domain.ErrNotFound if no row was deleted,
+// or domain.ErrPlantInUse if the ON DELETE RESTRICT foreign key from plantings
+// fires (a backstop for the service's own count check under a concurrent insert).
+func (d *DB) DeletePlant(ctx context.Context, id int64) error {