feat: Phase 2 — chat templates, reasoning parser, collapsible TUI, mouse support

- internal/llama/template.go: ChatML/Llama3 template engine with stop tokens
- internal/agent/reasoning.go: parse <think>/<reasoning> tags from LLM output
- companion/promptbuilder.go: output structured BuildResult, add date/time context
- agent/agent.go: wire templates + reasoning split into message loop
- storage: add reasoning TEXT column to messages table + migration
- channel/tui.go: collapsible reasoning (tab toggle), mouse scroll, polished dimmed style
- config: CHAT_TEMPLATE env var (chatml|llama3|none)
- plan.md: mark Phase 2 complete, add themes TODO

internal/config/config.go

@@ -36,6 +36,9 @@ type Config struct {
 	MemoryTopK     int
 	MemoryMinScore float64
 
+	// Chat template
+	ChatTemplate string
+
 	// Embedding
 	EmbeddingModel string
 
@@ -76,6 +79,8 @@ func Load() *Config {
 		MemoryTopK:     getEnvInt("MEMORY_TOP_K", 5),
 		MemoryMinScore: getEnvFloat("MEMORY_MIN_SCORE", 0.6),
 
+		ChatTemplate: getEnv("CHAT_TEMPLATE", "chatml"),
+
 		EmbeddingModel: getEnv("EMBEDDING_MODEL", ""),
 
 		TraitChangeMaxDaily:   getEnvFloat("TRAIT_CHANGE_MAX_DAILY", 0.005),
@@ -104,6 +109,11 @@ func (c *Config) Validate() error {
 	if c.DiaryHour < 0 || c.DiaryHour > 23 {
 		return fmt.Errorf("DIARY_HOUR must be 0-23")
 	}
+	switch c.ChatTemplate {
+	case "chatml", "llama3", "none":
+	default:
+		return fmt.Errorf("CHAT_TEMPLATE must be chatml, llama3, or none")
+	}
 	return nil
 }