EncounterLibraryRow shows global party count as if it were per-encounter

[gwillish]

EncounterAndPartyRootView.swift:189 passes partyCount (the global activePartyPlayers.count, :66) into every row as playerCount, which EncounterLibraryRow uses to compute the difficulty/BP rating (EncounterLibraryRow.swift:22–32).

Consequences:

• Every row shows a rating against the current party — identical across rows.
• All rows recompute at once when the party changes, causing list-wide reflow.
• The subtitle appears/disappears depending on whether all adversaries resolve in the compendium (EncounterLibraryRow.swift:25), so row heights vary with load timing.

The value is real and useful, but attributing it per-row implies a per-encounter number that does not exist.

Acceptance

• Either (a) label the rating explicitly as "vs current party," or (b) show a per-encounter metric (e.g. adversary count). Decide which here.
• Row height should not depend on compendium load timing.

Filed from architecture review.