When a product no longer appears in a successful scrape for its
retailer+caliber, mark it out of stock. After each scrape cycle, hard
delete any product whose last_seen_at is older than 30 days (snapshots
cascade via FK). A zero-result scrape leaves existing listings alone so
a parse failure or transient site glitch can't nuke the catalog.
- Add subsonic boolean field to products with composite filter indexes
- Add TextDetector utility for detecting subsonic/casing from product titles
- Wire TextDetector into SgAmmo (casing + subsonic) and LuckyGunner (subsonic + fallback casing)
- Extend latest_prices_for_caliber with casing, grain_weight, and subsonic filter options
- Add distinct_grain_weights_for_caliber and distinct_casings_for_caliber queries
- Add filter UI with toggleable casing, grain weight, and subsonic buttons
- Add grain weight column and subsonic badge to product table
- Refresh filter options on PubSub price updates for real-time UI
- Implement Target Sports USA scraper with 18 caliber mappings
- Display all prices in dollar format ($0.38 instead of 38¢)
