Add Flyway migrations V001-V019 for all 18 tables

V001: pgcrypto + citext extensions, trigger_set_updated_at function.
V002-V019: tables in FK dependency order per data model v1.1.

Spec fixes incorporated:
- recipe: added created_at/updated_at (spec says all mutable tables
  carry audit timestamps, but ERD omitted them)
- shopping_list: added household_id FK for HouseholdContext scoping
- shopping_list_item: added checked_by FK (API returns checkedBy)
- cooking_log: omitted phantom week_plan_slot_id (in FK map but
  absent from ERD, API, and all journeys)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/resources/db/migration/V009__create_recipe.sql

@@ -0,0 +1,19 @@
+CREATE TABLE recipe (
+    id                  uuid        PRIMARY KEY DEFAULT gen_random_uuid(),
+    household_id        uuid        NOT NULL REFERENCES household (id) ON DELETE CASCADE,
+    name                varchar(200) NOT NULL,
+    serves              smallint    NOT NULL CHECK (serves BETWEEN 1 AND 20),
+    cook_time_min       smallint    NOT NULL CHECK (cook_time_min >= 0),
+    effort              varchar(10) NOT NULL CHECK (effort IN ('easy', 'medium', 'hard')),
+    is_child_friendly   boolean     NOT NULL DEFAULT false,
+    hero_image_url      varchar(500),
+    deleted_at          timestamptz,
+    created_at          timestamptz NOT NULL DEFAULT now(),
+    updated_at          timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX idx_recipe_household ON recipe (household_id) WHERE deleted_at IS NULL;
+
+CREATE TRIGGER set_recipe_updated_at
+    BEFORE UPDATE ON recipe
+    FOR EACH ROW EXECUTE FUNCTION trigger_set_updated_at();