Spell cards repainted, VS popup goes size-aware, Empower as a strength-set, enemy row-seeking difficulty lever

Spell-card visuals + single-source school label. Cards are repainted for the new element set, and the school label on a card pulls from one source instead of being duplicated per-card — so renames propagate cleanly.

Spell descriptions: composed strategic copy. Spell descriptions are no longer one-size-fits-all; they're composed per-hero, with that hero's range and the list of sigils needed to pre-craft the spell. Reading a card now tells you what it costs to set up and where the hero can place it.

VS popup goes size-aware. The pre-fight VS popup detects screen size: mini spell cards on phones, compact on larger, two-up scrolling. The same popup stops looking cramped on phones and stretched on desktop.

Empower: strength-set duration. Empower now sets strength for N turns instead of stacking with itself per cast, with a pre-craft sigil popup added to the showcase scene so the new model reads from the card.

Difficulty lever: enemy row-seeking movement, default on. Enemies used to hold the row they spawned on. Now they move toward the row they want to be in to hit their target. Default on, gated behind a lever so it can be turned off if testing wants the old behaviour.

Library Student NPC art. The new Library Student NPC (split off from Digsite Student) gets her art.