fix(game): resolve battles ship by ship, matching the combat rules

The battle engine diverged from the documented combat model
(game/rules.txt "Сражения") in three ways:

- the destruction roll was inverted (rand >= p), so a near-certain hit
  destroyed its target only ~(1-p) of the time;
- a whole group fired as a single ship (Armament shots per round)
  regardless of its ship count, so fleet size never affected offence;
- the defending mass used the whole group's full mass instead of one
  target ship's, weakening grouped ships' shields by ~Number^(1/3).

SingleBattle now resolves ship by ship: every living ship fires once per
round in random order across all groups, each gun targets a random enemy
ship (weighted by group size), and the destruction roll matches the
documented probability. FilterBattleOpponents evaluates per-ship mass.

Also fixes opponent-map initialisation in ProduceBattles that kept only
an attacker's last opponent.

The rules already describe this model, so no documentation change is
needed. Tests: per-ship one-sided wipe, destruction-roll direction, and
the updated per-ship-mass probability expectation.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

game/internal/controller/controller_export_test.go

@@ -149,3 +149,7 @@ func (c *Cache) WipeRace(ri int) {
 func (c *Cache) UnsafeDeleteShipGroup(sgi int) {
 	c.unsafeDeleteShipGroup(sgi)
 }
+
+func DestructionRoll(probability float64) bool {
+	return destructionRoll(probability)
+}