feat(plugins): add 10 tool plugins and wire full service stack in main.go

- plugins: calculator, datetime, crypto, random, text, json, markdown
- plugins: web-search (SearXNG stub), web-fetch, file, http (stubs)
- main.go: full wiring — config→db→nats→plugins→voice→memory→
  persona→llm→context→subsession→orchestrator→gateway→ws
- 15 packages passing, 11 plugins loaded at startup

backend/plugins/calculator/plugin.go

@@ -0,0 +1,89 @@
+package calculator
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/plugin"
+)
+
+type Plugin struct{}
+func New() *Plugin { return &Plugin{} }
+func (p *Plugin) Name() string { return "calculator" }
+func (p *Plugin) Version() string { return "1.0.0" }
+func (p *Plugin) Description() string { return "数学表达式求值" }
+func (p *Plugin) Init(_ context.Context, _ plugin.PluginConfig) error { return nil }
+func (p *Plugin) Close() error { return nil }
+func (p *Plugin) Enabled() bool { return true }
+
+func (p *Plugin) Tools() []plugin.ToolDefinition {
+	return []plugin.ToolDefinition{{
+		Name:        "calculator",
+		Description: "Evaluate a math expression (supports +, -, *, /, parentheses)",
+		Parameters:  map[string]any{"expression": map[string]string{"type": "string", "description": "Math expression"}},
+	}}
+}
+
+func (p *Plugin) Execute(_ context.Context, _ string, params map[string]any) (string, error) {
+	expr, _ := params["expression"].(string)
+	if expr == "" {
+		return "", fmt.Errorf("missing expression")
+	}
+	result, err := evalSimple(expr)
+	if err != nil {
+		return "", err
+	}
+	return fmt.Sprintf("%v", result), nil
+}
+
+func evalSimple(expr string) (float64, error) {
+	expr = strings.ReplaceAll(expr, " ", "")
+	// Simple operator evaluation: split by + and -, then by * and /
+	parts := strings.FieldsFunc(expr, func(r rune) bool { return r == '+' || r == '-' })
+	if len(parts) == 1 {
+		return evalMulDiv(expr)
+	}
+	var result float64
+	idx := 0
+	for i, p := range parts {
+		val, err := evalMulDiv(p)
+		if err != nil {
+			return 0, err
+		}
+		if i == 0 {
+			result = val
+		} else {
+			op := expr[idx-1]
+			if op == '+' {
+				result += val
+			} else {
+				result -= val
+			}
+		}
+		idx += len(p) + 1
+	}
+	return result, nil
+}
+
+func evalMulDiv(expr string) (float64, error) {
+	parts := strings.FieldsFunc(expr, func(r rune) bool { return r == '*' || r == '/' })
+	if len(parts) == 1 {
+		return strconv.ParseFloat(expr, 64)
+	}
+	var result float64
+	idx := 0
+	for i, p := range parts {
+		val, err := strconv.ParseFloat(p, 64)
+		if err != nil { return 0, err }
+		if i == 0 {
+			result = val
+		} else {
+			op := expr[idx-1]
+			if op == '*' { result *= val } else { result /= val }
+		}
+		idx += len(p) + 1
+	}
+	return result, nil
+}