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/routing/log.go

@@ -13,7 +13,7 @@ import (
 type LogEntry struct {
 	SessionID   string
 	Skill       string // the original skill the call routed (e.g., "review")
-	Decision    string // "local" or "claude" or "claude_fallback"
+	Decision    string // "local" or "thinking" or "thinking_fallback"
 	Message     string // free-form, e.g. "model=qwen35, pass_rate=0.94"
 	ProjectRoot string
 	DurationMs  int64