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/file/plugin.go

@@ -1,19 +1,132 @@
 package file
+
 import (
-    "context"
-    "git.yeij.top/AskaEth/Cyrene_v2/internal/plugin"
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/plugin"
 )
-type Plugin struct{}
+
+// Plugin provides sandboxed file read/write inside the configured data directory.
+type Plugin struct {
+	dataDir string
+}
+
 func New() *Plugin { return &Plugin{} }
-func (p *Plugin) Name() string { return "file" }
-func (p *Plugin) Version() string { return "1.0.0" }
+
+func (p *Plugin) Name() string        { return "file" }
+func (p *Plugin) Version() string     { return "1.0.0" }
 func (p *Plugin) Description() string { return "文件操作" }
-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) Close() error        { return nil }
+func (p *Plugin) Enabled() bool       { return p.dataDir != "" }
+
+func (p *Plugin) Init(_ context.Context, cfg plugin.PluginConfig) error {
+	p.dataDir = cfg.DataDir
+	if p.dataDir == "" {
+		p.dataDir = "data/files"
+	}
+	return os.MkdirAll(p.dataDir, 0o755)
+}
+
 func (p *Plugin) Tools() []plugin.ToolDefinition {
-    return []plugin.ToolDefinition{{Name:"file", Description:"读写文件", Parameters:map[string]any{"path": map[string]string{"type":"string"}}}}
+	return []plugin.ToolDefinition{
+		{
+			Name:        "file_read",
+			Description: "Read a text file from the data directory.",
+			Parameters: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"path": map[string]string{"type": "string", "description": "Relative path inside the data directory"},
+				},
+				"required": []string{"path"},
+			},
+		},
+		{
+			Name:        "file_write",
+			Description: "Write text to a file in the data directory (overwrites).",
+			Parameters: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"path":    map[string]string{"type": "string", "description": "Relative path inside the data directory"},
+					"content": map[string]string{"type": "string", "description": "Text content to write"},
+				},
+				"required": []string{"path", "content"},
+			},
+		},
+		{
+			Name:        "file_list",
+			Description: "List files in the data directory (or a subdirectory).",
+			Parameters: map[string]any{
+				"type": "object",
+				"properties": map[string]any{
+					"path": map[string]string{"type": "string", "description": "Relative directory path (default: root)"},
+				},
+			},
+		},
+	}
 }
-func (p *Plugin) Execute(_ context.Context, _ string, _ map[string]any) (string, error) {
-    return "[文件] 功能占位", nil
+
+func (p *Plugin) Execute(_ context.Context, toolName string, params map[string]any) (string, error) {
+	rel, _ := params["path"].(string)
+	path, err := p.resolve(rel)
+	if err != nil {
+		return "", err
+	}
+
+	switch toolName {
+	case "file_read":
+		data, err := os.ReadFile(path)
+		if err != nil {
+			return "", fmt.Errorf("read: %w", err)
+		}
+		text := string(data)
+		if runes := []rune(text); len(runes) > 4000 {
+			text = string(runes[:4000]) + "\n…（文件过长已截断）"
+		}
+		return text, nil
+
+	case "file_write":
+		content, _ := params["content"].(string)
+		if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+			return "", err
+		}
+		if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+			return "", fmt.Errorf("write: %w", err)
+		}
+		return fmt.Sprintf("已写入 %s（%d 字节）", rel, len(content)), nil
+
+	case "file_list":
+		entries, err := os.ReadDir(path)
+		if err != nil {
+			return "", fmt.Errorf("list: %w", err)
+		}
+		if len(entries) == 0 {
+			return "（空目录）", nil
+		}
+		var sb strings.Builder
+		for _, e := range entries {
+			name := e.Name()
+			if e.IsDir() {
+				name += "/"
+			}
+			sb.WriteString(name + "\n")
+		}
+		return sb.String(), nil
+	}
+	return "", fmt.Errorf("unknown tool %q", toolName)
+}
+
+// resolve maps a relative path into the sandbox and rejects escapes.
+func (p *Plugin) resolve(rel string) (string, error) {
+	clean := filepath.Clean("/" + rel) // force relative interpretation
+	full := filepath.Join(p.dataDir, clean)
+	root, _ := filepath.Abs(p.dataDir)
+	abs, _ := filepath.Abs(full)
+	if abs != root && !strings.HasPrefix(abs, root+string(filepath.Separator)) {
+		return "", fmt.Errorf("path escapes data directory")
+	}
+	return full, nil
 }