refactor(routing): rename local/claude to fast/thinking model pair

The routing decision is about reasoning capacity, not cost or provider.
Fast model (koala/qwen35-9b-fast) handles high-pass-rate calls; thinking
model (iguana/gemma4-26b) handles low-pass-rate calls. Removes the
implicit Anthropic dependency from the routing pod — both models go
through LiteLLM.

Renames: HYPERGUILD_LOCAL_MODEL → HYPERGUILD_FAST_MODEL,
HYPERGUILD_CLAUDE_MODEL → HYPERGUILD_THINKING_MODEL,
Router.LocalModel → FastModel, Router.ClaudeModel → ThinkingModel,
log decision "claude_fallback" → "thinking_fallback".

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

internal/config/routing.go

@@ -14,8 +14,8 @@ type RoutingConfig struct {
 	LiteLLMBaseURL     string  // LITELLM_BASE_URL, default http://piguard:4000
 	LiteLLMAPIKey      string  // LITELLM_API_KEY
 	BrainURL           string  // BRAIN_URL, default http://ingestion.supervisor:3300
-	LocalModel         string  // HYPERGUILD_LOCAL_MODEL, default qwen35
-	ClaudeModel        string  // HYPERGUILD_CLAUDE_MODEL, default claude-sonnet-4-6
+	FastModel          string  // HYPERGUILD_FAST_MODEL, default koala/qwen35-9b-fast
+	ThinkingModel      string  // HYPERGUILD_THINKING_MODEL, default iguana/gemma4-26b
 	// RouteLocalFloor and RouteLocalCeil intentionally invert the usual
 	// floor < ceil mathematical convention: Floor (default 0.90) is the
 	// UPPER boundary — at/above it, always route local; Ceil (default 0.70)
@@ -34,8 +34,8 @@ func LoadRouting() (RoutingConfig, error) {
 		LiteLLMBaseURL: envOr("LITELLM_BASE_URL", "http://piguard:4000"),
 		LiteLLMAPIKey:  os.Getenv("LITELLM_API_KEY"),
 		BrainURL:       envOr("BRAIN_URL", "http://ingestion.supervisor:3300"),
-		LocalModel:     envOr("HYPERGUILD_LOCAL_MODEL", "qwen35"),
-		ClaudeModel:    envOr("HYPERGUILD_CLAUDE_MODEL", "claude-sonnet-4-6"),
+		FastModel:      envOr("HYPERGUILD_FAST_MODEL", "koala/qwen35-9b-fast"),
+		ThinkingModel:  envOr("HYPERGUILD_THINKING_MODEL", "iguana/gemma4-26b"),
 	}
 
 	floor, err := parseFloatEnv("HYPERGUILD_ROUTE_LOCAL_FLOOR", 0.90)