feat(rules): spell components + deafened verbal failure and arcane spell failure rolls

- SpellSpec.components (frozenset of V/S/M/F/DF, JSON key accepting the RAW
  string notation "V, S, M/DF" or a token list; slash = alternative; unknown
  token is a data error). Default empty = not encoded yet -> no failure.
- Combatant.armor_spell_failure (0-100 percent, authored on the JSON - the
  model has no equipment) and arcane_caster (divine casters never incur ASF);
  both load directly through load_combatant.
- _cast_spell: after the start-of-casting gates and before delivery, two
  conditional d100 rolls (convention mirrors the concealment roll, <=):
  deafened + V component spoils the spell on <=20 (SRD cast-a-spell.md);
  arcane_caster + S component + armor_spell_failure > 0 fails the spell on
  <= the ASF percent (SRD arcane-spells-and-armor.md). The slot stays spent
  (mirrors the concentration fizzle). No condition -> no roll: the RNG
  stream is bit-identical for every current combat (registry encodes no
  components yet - full encoding is a follow-up task).
- Observation: spell summary gains "components" (sorted tuple), combatant
  snapshot gains "armor_spell_failure"/"arcane_caster"; README documents
  the keys and the two former out-of-scope bullets now describe the modeled
  rule with its data-encoding follow-up.
- Data smoke test: lich arcane_caster true / ASF 0, oni arcane_caster false.
- tests/test_spell_failure.py: 21 tests (parsing, thresholds <=20 / <=ASF,
  divine/no-ASF/no-component never roll, roll order, slot stays spent,
  observation keys). Golden transcripts unchanged.

src/pf1e_simulator/models.py

@@ -322,6 +322,16 @@ class Combatant(_FrozenModel):
     metamagic_feats: list[str] = Field(default_factory=list)  # e.g. Empower/Maximize/Extend Spell
     spells: list[str] = Field(default_factory=list)
     spell_resistance: int = 0
+    # PF1e (SRD, Magic - Arcane Spells and Armor): the armor/shield worn
+    # imposes an arcane spell failure chance (percent, 0-100) on arcane
+    # spells with a somatic component. The model has no equipment, so the
+    # chance is authored directly on the combatant JSON.
+    # rules/prpg-core-rulebook/arcane-spells-and-armor.md
+    armor_spell_failure: int = Field(default=0, ge=0, le=100)
+    # True when the combatant's spellcasting is arcane (sorcerer, wizard,
+    # magus...) - only arcane casters incur armor spell failure; divine
+    # casters (cleric, druid...) wear any armor freely.
+    arcane_caster: bool = False
     resistances: dict[str, int] = Field(default_factory=dict)
     immunities: tuple[str, ...] = ()
     # PF1e (SRD "Surprise"): "If some but not all of the combatants are aware