feat(engine): voice pipeline Phase 1 — composition engine and data model

Add the voice pipeline composition engine (D-138 Spike 2, Phase 1):

- voice/prompt_builder.rs: full prompt assembly from culture profile,
  tell state, and base text. Handles occasional injection gating,
  epistemic marker extraction, content-length-gated tell injection.
  16 unit tests.

- blueprint.rs: CultureProfile gains voice_persona, voice_examples,
  occasional_injections fields. NpcBlueprint gains tell_behaviors.
  OccasionalInjection struct with kind discriminator (oath/faith/
  hesitancy/etc), frequency, and tell-suppression gating.

- culture-krenn.ron: v2 voice injector from Spike 1 — persona block,
  3 examples, oath injection at 0.25 frequency.

- D-138 amended: Phi-3 dropped entirely, exact Gemma 2B provenance
  documented. Model file renamed to gemma2.gguf.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/bin/generator_spike.rs

@@ -245,6 +245,9 @@ fn hardcoded_krenn_culture() -> CultureProfile {
             favored_traits: vec![PersonalityTrait::Bold, PersonalityTrait::Honest, PersonalityTrait::Curious],
             disfavored_traits: vec![PersonalityTrait::Reclusive, PersonalityTrait::Deceptive],
         },
+        voice_persona: None,
+        voice_examples: vec![],
+        occasional_injections: vec![],
     }
 }
 
@@ -579,6 +582,7 @@ fn generate_npc_blueprint(
         observable_behaviors,
         cultural_markers,
         relationships: vec![],
+        tell_behaviors: vec![],
     }
 }