Housing Decor Guide

### Added
- Shopping List import: housing.wowdb.com builds can now be exported
  directly into HDG. Click "Export Shopping List" on any build at
  housing.wowdb.com, paste the string into HDG's Import dialog, and
  HDG handles the rest -- attribution banner, clickable build URL,
  and per-item quantities all populate from the header. No mode
  switch required.
- Shopping List import: auto-resolve missing vendors. When an imported
  entry has no vendor specified but the item is flagged as
  vendor-sourced in HDG's catalog, the importer now picks the first
  matching vendor from HDG's vendor index. External tools no longer
  need to know vendor IDs.
- Preview: new "Dyeable" category filter alongside "Dyed" -- shows
  every decor that can accept dyes (whether or not you own a dyed
  copy yet).
- Useful Collections: new "Trophies" pinned collection. Includes
  every unique-trophy decor and every Preyseeker effigy -- the rare
  trophies earned through hard PVE content (raids, dungeons, prey
  hunts).
- Trainers: Cost / Method column widened so longer cost strings
  ("150 Artisan Alchemist's Moxie + Voidlight Marl") fit on one
  line. Map All / Clear button widths fitted to label text.

### Changed
- Internal: housing-catalog access centralised. All UI surfaces
  (Acquire, Preview, Styles, House Editor, Data, zone scanner) now
  read from one persisted snapshot instead of calling Blizzard's
  catalog API directly. Restored from SavedVariables on /reload for
  instant first paint; rebuilt automatically on patch crossing.
  Background verification sweep confirms saved data on each
  window-open. Refresh button performs a full reset. Two redundant
  per-tab searchers and three per-tab catalog caches retired.
- Dye-variant ownership: players who only own dyed variants of a
  decor are now correctly flagged as collecting that decorID
  (previously the base entry's zero-count masked it). Dyed variants
  rebuilt via Blizzard's variant API after the 12.0.5 catalog API
  change removed subtypeIdentifier from searcher results -- the
  House Editor's per-variant cards (with mini dye swatches) work
  again, and clicking a variant card places that specific variant.
- Alts: profession-recipe tracking now scans by profession-with-decor
  list rather than the player's primary slot indexes. Cooking and
  other secondary professions are tracked even when not in the
  player's primary slots.
- Shopping List import: hint text updated to "Paste an HDG, Wowhead
  or housing.wowdb.com string".