refactor: remove all backtest module code and references

Delete backtest/ engine (19 files), api/backtest.go, store/backtest.go,
web backtest components (7 files), API client, types, docs, screenshot.
Clean all backtest references from main.go, api/server.go, store/store.go,
App.tsx, HeaderBar.tsx, LandingPage.tsx, translations, README and docs.

docs/plans/2026-03-06-telegram-agent-redesign.md

@@ -243,7 +243,6 @@ s.route(protected, "GET", "/statistics",         "Trading statistics (?trader_id
 Note: keep the existing special-case handlers that don't use `s.route` unchanged:
 - `api.Any("/health", ...)` — health check, no need to document
 - `api.GET("/crypto/...")` — crypto/encryption routes, bot doesn't need these
-- `backtest.*` routes (registered separately) — add descriptions to the backtest group similarly
 
 **Step 3: Build**
 

docs/plans/2026-03-06-telegram-bot.md

@@ -993,7 +993,7 @@ func Start(cfg *config.Config, st *store.Store, tm *manager.TraderManager) {
 
 	logger.Infof("🤖 Telegram bot started: @%s", bot.Self.UserName)
 
-	// Build the LLM client for intent parsing (use DeepSeek by default, same as backtest)
+	// Build the LLM client for intent parsing (use DeepSeek by default)
 	llmClient := mcp.New()
 	// Configure with whatever key is available in env (intent parsing is lightweight)
 	// The service layer will use store to get user-configured models for actual trading