feat: Add Telegram AI Assistant (moltbot-nofx integration)

- Add assistant package with AI Agent runtime
  - agent.go: Core agent loop with tool calling
  - session.go: Conversation memory management
  - tool.go: Tool interface and base implementation
  - trading_tools.go: Trading-specific tools (13 tools)
  - prompts.go: Trading expert system prompts (EN/ZH)

- Add telegram package for Telegram bot integration
  - bot.go: Telegram bot with rate limiting & access control
  - config.go: Environment-based configuration

- Update main.go to initialize Telegram bot on startup
- Update .env.example with new configuration options
- Add gopkg.in/telebot.v3 dependency

Trading tools available:
- Query: get_balance, get_positions, list_traders, get_trader_status
- Control: start_trader, stop_trader
- Trading: get_market_price, open_long, open_short, close_position
- Config: list_strategies, list_exchanges, list_ai_models

assistant/tool.go

@@ -0,0 +1,47 @@
+package assistant
+
+import (
+	"context"
+	"encoding/json"
+)
+
+// Tool represents a callable tool that the AI agent can use
+type Tool interface {
+	// Name returns the tool's unique identifier
+	Name() string
+
+	// Description returns a human-readable description for the AI
+	Description() string
+
+	// ParameterSchema returns JSON schema for the tool's parameters
+	ParameterSchema() string
+
+	// Execute runs the tool with the given arguments
+	Execute(ctx context.Context, args json.RawMessage) (interface{}, error)
+}
+
+// BaseTool provides common functionality for tools
+type BaseTool struct {
+	ToolName        string
+	ToolDescription string
+	ToolSchema      string
+	ExecuteFunc     func(ctx context.Context, args json.RawMessage) (interface{}, error)
+}
+
+func (t *BaseTool) Name() string        { return t.ToolName }
+func (t *BaseTool) Description() string { return t.ToolDescription }
+func (t *BaseTool) ParameterSchema() string { return t.ToolSchema }
+
+func (t *BaseTool) Execute(ctx context.Context, args json.RawMessage) (interface{}, error) {
+	return t.ExecuteFunc(ctx, args)
+}
+
+// NewTool creates a simple tool from a function
+func NewTool(name, description, schema string, fn func(ctx context.Context, args json.RawMessage) (interface{}, error)) Tool {
+	return &BaseTool{
+		ToolName:        name,
+		ToolDescription: description,
+		ToolSchema:      schema,
+		ExecuteFunc:     fn,
+	}
+}