feat(items): add base price and support usage in creation defaults

Add `base_price` to items schema, API, and edit history
Display and edit base price in item details and forms
Add `clearable` prop to TagsSelect for optional single selections
Include usage in item creation session defaults

backend/db/schema.sql

@@ -976,6 +976,7 @@ CREATE TABLE IF NOT EXISTS items (
   id integer GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY,
   name text NOT NULL UNIQUE,
   details text NOT NULL DEFAULT '',
+  base_price integer,
   category_key text NOT NULL DEFAULT 'other',
   usage_key text,
   category_id integer REFERENCES item_categories(id),
@@ -1220,9 +1221,14 @@ ALTER TABLE life_tags
 
 ALTER TABLE items
   ADD COLUMN IF NOT EXISTS details text NOT NULL DEFAULT '',
+  ADD COLUMN IF NOT EXISTS base_price integer,
   ADD COLUMN IF NOT EXISTS category_key text,
   ADD COLUMN IF NOT EXISTS usage_key text;
 
+UPDATE items
+SET base_price = NULL
+WHERE base_price < 0;
+
 ALTER TABLE ancient_artifacts
   ADD COLUMN IF NOT EXISTS image_path text NOT NULL DEFAULT '';
 
@@ -1301,10 +1307,12 @@ ALTER TABLE items
 
 ALTER TABLE items
   DROP CONSTRAINT IF EXISTS items_display_id_positive,
+  DROP CONSTRAINT IF EXISTS items_base_price_check,
   DROP CONSTRAINT IF EXISTS items_category_key_check,
   DROP CONSTRAINT IF EXISTS items_usage_key_check;
 
 ALTER TABLE items
+  ADD CONSTRAINT items_base_price_check CHECK (base_price IS NULL OR base_price >= 0),
   ADD CONSTRAINT items_category_key_check CHECK (category_key IN (
     'furniture',
     'misc',