Skills, auto-attack, aura and chain lightning rework, Esc, cache fix

- Skill bar: no art selection; slot 0 is the right-click art, keys 0-6 cast
  slots directly; cooldown labels in exact seconds; slot 0 set apart.
- Arts regenerate on their own (casting no longer refills the group).
- Auto-attack after targeting or casting at a hostile creature, at the speed
  of a held button.
- Auras can be recast while active (renew, no second visual).
- Blicke wie Klingen hits every enemy in range, physical, with life leech.
- Blitzschlag steers the game's own chain: 3 + level/5 hits, 1 + level/10
  chains, re-hits a lone enemy.
- Weapon sets: click selects, drag only from the selected set; the leftmost
  set is clickable (signed hit tests).
- Esc closes open windows before opening the game menu.
- HUD: standalone buttons and texts are centred.
- Record cache sized for widened views (town lag while walking).
- Shared game code: orders, fx events, text drawing, cooldowns, effects.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/art-regen.md

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+# Art regeneration (`src/mods/artregen.cpp`, `game::GetArtCooldown`)
+
+Goal (user, 2026-10-15): casting an art no longer affects the cooldowns of
+other arts; the cooldown labels show exact seconds.
+
+## How the game regenerates arts (measured 2026-10-15)
+
+Cooldown entries: see `src/game/engine/arts.h` (cCreatureArts +0x102,
+0x16 bytes each: group, art, level, bonus levels, total, speed factor,
+remaining). Found with a hardware write watch on one entry's remaining time:
+
+- countdown, every creature update (`0x562998`):
+  `remaining -= speed factor * rate * seconds`, rate = cCreatureArts +0xee
+  (magic group, Energieblitze) or +0xf2; clamped to 0..total;
+- casting an art: the cast code computes the art's regeneration
+  (`cCreatureArts::RegenFor` `0x582710`) and adds it with
+  `cCreatureArts::AddGroupRegen` (`0x562330`, (amount, group, filter)) to
+  **every** entry of the group (combat arts / magic), capped at each total:
+  one cast puts the whole group into regeneration. Flags +0x148 & 8 / & 4 cut
+  the amount to 80 % for the magic / combat group; Flammenwerfer, Meteor,
+  Kanone and Energieblitze always count as magic. A combo (creature +0x2b4,
+  arts +0x59) or group 3 takes another branch (combo slots at +0x10e);
+- the speed factor (+0xe) is reset by the stats recalculation (`0x579b7d`,
+  `0x570fad`), the level byte +7 raised by item bonuses (`0x581e40`, which
+  adds the change of the total to the remaining time).
+
+## The mod
+
+For player heroes, an AddGroupRegen call right after RegenFor (same thread)
+adds the amount to the cast art's entry only. Other calls (negative amounts,
+filters, combos, other callers) go to the game. Labels: seconds =
+remaining / (speed factor * rate).