feat(plugins): implement web-search, web-fetch, http and file tools

- web-search: real SearXNG /search?format=json query, top-5 formatted
  results (was a 'not configured' stub)
- web-fetch: fetch page, strip scripts/styles/tags, truncate to 4000
  runes for the LLM context
- http: generic request tool (GET/POST/PUT/DELETE/PATCH) with scheme
  and method validation, status + truncated body
- file: sandboxed read/write/list inside the data directory with path
  escape rejection; split into file_read/file_write/file_list
- all tool schemas converted to proper JSON Schema; httptest/tempdir
  tests for each plugin

backend/plugins/web-search/plugin.go

@@ -1,19 +1,91 @@
 package websearch
+
 import (
-    "context"
-    "git.yeij.top/AskaEth/Cyrene_v2/internal/plugin"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/plugin"
 )
-type Plugin struct{ searxngURL string }
-func New(url string) *Plugin { return &Plugin{searxngURL: url} }
-func (p *Plugin) Name() string { return "web-search" }
-func (p *Plugin) Version() string { return "1.0.0" }
+
+type Plugin struct {
+	searxngURL string
+	client     *http.Client
+}
+
+func New(url string) *Plugin {
+	return &Plugin{searxngURL: strings.TrimRight(url, "/"), client: &http.Client{Timeout: 15 * time.Second}}
+}
+
+func (p *Plugin) Name() string        { return "web-search" }
+func (p *Plugin) Version() string     { return "1.0.0" }
 func (p *Plugin) Description() string { return "网络搜索" }
 func (p *Plugin) Init(_ context.Context, _ plugin.PluginConfig) error { return nil }
-func (p *Plugin) Close() error { return nil }
-func (p *Plugin) Enabled() bool { return p.searxngURL != "" }
+func (p *Plugin) Close() error        { return nil }
+func (p *Plugin) Enabled() bool       { return p.searxngURL != "" }
+
 func (p *Plugin) Tools() []plugin.ToolDefinition {
-    return []plugin.ToolDefinition{{Name:"web_search", Description:"互联网搜索", Parameters:map[string]any{"query": map[string]string{"type":"string"}}}}
+	return []plugin.ToolDefinition{{
+		Name:        "web_search",
+		Description: "Search the internet via SearXNG. Returns top results with title, URL and snippet.",
+		Parameters: map[string]any{
+			"type": "object",
+			"properties": map[string]any{
+				"query": map[string]string{"type": "string", "description": "Search query"},
+			},
+			"required": []string{"query"},
+		},
+	}}
 }
-func (p *Plugin) Execute(_ context.Context, _ string, _ map[string]any) (string, error) {
-    return "[搜索] 引擎未配置", nil
+
+type searxResult struct {
+	Title   string `json:"title"`
+	URL     string `json:"url"`
+	Content string `json:"content"`
+}
+
+func (p *Plugin) Execute(ctx context.Context, _ string, params map[string]any) (string, error) {
+	query, _ := params["query"].(string)
+	if query == "" {
+		return "", fmt.Errorf("missing query")
+	}
+
+	reqURL := fmt.Sprintf("%s/search?q=%s&format=json", p.searxngURL, url.QueryEscape(query))
+	req, err := http.NewRequestWithContext(ctx, "GET", reqURL, nil)
+	if err != nil {
+		return "", err
+	}
+
+	resp, err := p.client.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("search request: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		return "", fmt.Errorf("search API %d", resp.StatusCode)
+	}
+
+	var result struct {
+		Results []searxResult `json:"results"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
+		return "", fmt.Errorf("parse results: %w", err)
+	}
+	if len(result.Results) == 0 {
+		return fmt.Sprintf("搜索 %q 没有结果", query), nil
+	}
+
+	var sb strings.Builder
+	fmt.Fprintf(&sb, "搜索 %q 的结果：\n", query)
+	for i, r := range result.Results {
+		if i >= 5 {
+			break
+		}
+		fmt.Fprintf(&sb, "%d. %s\n   %s\n   %s\n", i+1, r.Title, r.URL, r.Content)
+	}
+	return sb.String(), nil
 }