Seasonal Goals

### Where to get this
- Cells now show **where to obtain** a tier appearance. Hover any non-collected
  cell for a compact "Drops from: <boss>" summary; red (missing) cells are now
  clickable and open the detail panel.
- The detail panel's **"Where to get this"** lists every item you can get for the
  look and where it drops, grouped **Raid** then **Dungeon**. The Raid group
  leads with the tier token, the curio (any tier slot), and any known matching
  accessory; convertible same-slot pieces follow as item rows (icon + name +
  boss/instance, hover tooltip, shift-click to link).
- Source data ships with the addon (`src/data_sources.lua` + generated
  `src/data_feeders.lua`), refreshed per season via `/sg discover all` and
  `/sg discover feeders` — no per-user setup. Convertible feeders cover the
  Encounter Journal's current-season pool (raids + the full M+ rotation,
  including legacy dungeons).