UX S6: race truth-up — wire Tiefling fire resist + best-fit hints

R22: replace race copy that promised mechanics the engine doesn't deliver.
- Tiefling: wire FireResist as a CombatModifier. Enemy main attack is
  halved when monster is FireAttacker-tagged; aoe_fire abilities are
  halved unconditionally; fire-tagged traps deal half damage to Tieflings.
  DnDMonsterTemplate carries FireAttacker; toCombatStats propagates it.
  Hand-authored fire entries tagged in dnd_bestiary.go (flameskull,
  magmin, azer, salamander, fire_elemental, emberlord_thyrak,
  young_red_dragon, infernax, belaxath).
- Open5e tuned generator derives FireAttacker from the highest-AvgDamage
  attack's DamageType (threshold AvgDamage>=5). 19 tuned monsters tag.
  Regenerated bestiary_tuned_data.go.
- Elf: drop "immune to sleep" (no sleep mechanic); reframe as keen
  senses + trance flavor.
- Half-Elf: drop "two bonus skill proficiencies" (no skill system);
  reframe as adaptable cross-cultural know-how.
- Tiefling copy: drop "bonus on CHA checks" (no checks); keep fire
  resistance with flavor framing.

R23: DnDRaceInfo grows a BestFit field; renderRaceMenu emits an
"_best with: …_" hint per race so spiky stat spreads (Orc -1/-1/-1)
read as specialist picks rather than a brick of penalties.

R24: dnd.go header comment for the caster classes now reflects the
shipped state (Playable=true, spell lists populated) instead of the
pre-Open5e scaffold language.

Tests: TestApplyRacePassives gains a FireResist column; new
TestTieflingFireResistance asserts ~0.5x ratio over a 300-trial sweep
against a FireAttacker enemy. Full suite green.

internal/plugin/dnd_passives.go

@@ -75,10 +75,9 @@ func clampNonNeg(x int) int {
 }
 
 // applyRacePassives sets the combat-impacting flags from the player's race.
-// Races whose passives apply to skill checks or non-combat scenarios
-// (Tiefling fire resist, Elf sleep immunity, Half-Elf bonus profs, Human
-// floating +1) are handled in their respective phases and have no combat
-// hook in Phase 3.
+// Elf "trance" (resilience flavor), Half-Elf "adaptable" (cross-cultural know-
+// how), and the Human floating +1 are non-combat or stat-only and have no
+// engine hook here.
 func applyRacePassives(stats *CombatStats, mods *CombatModifiers, c *DnDCharacter) {
 	switch c.Race {
 	case RaceHalfling:
@@ -87,6 +86,11 @@ func applyRacePassives(stats *CombatStats, mods *CombatModifiers, c *DnDCharacte
 		mods.RageReady = true
 	case RaceDwarf:
 		mods.PoisonResist = true
+	case RaceTiefling:
+		// Fiendish heritage: incoming fire damage is halved by the combat
+		// engine (enemy attack path + aoe_fire ability) and by the trap
+		// resolver (fire-tagged traps).
+		mods.FireResist = true
 	}
 }