feat(BE-115,116,117): implement chickin CRUD, approve logic, and stock availabilit

internal/database/migrations/20251019040246_create_stock_availabilities_table.up.sql

@@ -0,0 +1,15 @@
+CREATE TABLE stock_availabilities (
+    id BIGSERIAL PRIMARY KEY,
+    entity_type VARCHAR(50) NOT NULL,
+    entity_id BIGINT NOT NULL,
+    product_id BIGINT,
+    quantity NUMERIC(15, 3) NOT NULL DEFAULT 0,
+    reserved_quantity NUMERIC(15, 3) NOT NULL DEFAULT 0,
+    unit VARCHAR(20),
+    last_updated TIMESTAMPTZ DEFAULT now(),
+    created_at TIMESTAMPTZ DEFAULT now(),
+    deleted_at TIMESTAMPTZ
+);
+
+ALTER TABLE stock_availabilities
+ADD CONSTRAINT fk_product_id FOREIGN KEY (product_id) REFERENCES products (id);