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/crypto/plugin.go

@@ -0,0 +1,23 @@
+package crypto
+import (
+    "context"; "crypto/md5"; "crypto/sha256"; "encoding/hex"
+    "git.yeij.top/AskaEth/Cyrene_v2/internal/plugin"
+)
+type Plugin struct{}
+func New() *Plugin { return &Plugin{} }
+func (p *Plugin) Name() string { return "crypto" }
+func (p *Plugin) Version() string { return "1.0.0" }
+func (p *Plugin) Description() string { return "哈希加密" }
+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:"crypto", Description:"MD5/SHA256", Parameters:map[string]any{"algo":map[string]string{"type":"string"}, "text":map[string]string{"type":"string"}}}}
+}
+func (p *Plugin) Execute(_ context.Context, _ string, params map[string]any) (string, error) {
+    text,_ := params["text"].(string)
+    if algo,_ := params["algo"].(string); algo == "sha256" {
+        h := sha256.Sum256([]byte(text)); return hex.EncodeToString(h[:]), nil
+    }
+    h := md5.Sum([]byte(text)); return hex.EncodeToString(h[:]), nil
+}