fix(draft): Lore Seeker adds cube booster from surplus in cube drafts

[billyhewlett]

Problem

In cube drafts, Lore Seeker's effect ("after you draft this, you may add a
booster pack to the draft") calls addBooster(CardEdition), which opens a
set-selection dialog and injects a booster from an arbitrary retail set.
This breaks the cube draft's card pool contract: players draft a card from
outside the cube.

Background

In a cube draft, the number of cards used equals (players × packs × pack size).
The remainder of the cube's card pool sits unused after booster initialization.
For example, a 540-card cube with 8 players drafting 3 packs of 15 uses
8 × 3 × 15 = 360 cards, leaving 180 surplus. Lore Seeker should draw its
booster from this surplus rather than from a retail set.

Changes

UnOpenedProduct.java
Add getRemainingCards(): returns all cards still in the print sheets after
booster draws. Enables callers to inspect surplus without modifying state.

BoosterDraft.java

• Retain a reference (cubeProduct) to the cube's UnOpenedProduct during
  setupCustomDraft().
• After initializeBoosters() distributes all packs, snapshot remaining
  cards into a shuffled cubeSurplus list.
• Override addBooster() (no-arg) to draw a pack from cubeSurplus.
  Returns null when surplus is exhausted.

IBoosterDraft.java
Add default DraftPack addBooster() returning null as the base case for
non-cube draft implementations.

LimitedPlayer.java
In addSingleBoosterPack(), try draft.addBooster() first. If it returns
a pack (cube surplus available), use it. Fall back to the existing
set-selection dialog only for non-cube drafts or when surplus is exhausted.

Non-cube drafts

Unaffected. addBooster() returns null for all non-BoosterDraft
implementations, and the fallback path runs as before.

Testing

Draft with a cube containing Lore Seeker. Verify:

1. Drafting Lore Seeker adds a pack drawn from cube cards (not a retail set dialog).
2. After surplus is exhausted, falls back to the set-selection dialog.
3. Non-cube drafts with Lore Seeker continue to show the set dialog.