Feat: Initialize context engine CLI (#13776)

### What problem does this PR solve?

- Add multiple output format to ragflow_cli
- Initialize contextengine to Go module
  - ls datasets/ls files
  - cat file
  - search -d dir -q query

issue: #13714

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

internal/cli/contextengine/provider.go

@@ -0,0 +1,180 @@
+//
+//  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+package contextengine
+
+import (
+	stdctx "context"
+)
+
+// Provider is the interface for all context providers
+// Each provider handles a specific resource type (datasets, chats, agents, etc.)
+type Provider interface {
+	// Name returns the provider name (e.g., "datasets", "chats")
+	Name() string
+
+	// Description returns a human-readable description of the provider
+	Description() string
+
+	// Supports returns true if this provider can handle the given path
+	Supports(path string) bool
+
+	// List lists nodes at the given path
+	List(ctx stdctx.Context, path string, opts *ListOptions) (*Result, error)
+
+	// Search searches for nodes matching the query under the given path
+	Search(ctx stdctx.Context, path string, opts *SearchOptions) (*Result, error)
+
+	// Cat retrieves the content of a file/document at the given path
+	Cat(ctx stdctx.Context, path string) ([]byte, error)
+}
+
+// BaseProvider provides common functionality for all providers
+type BaseProvider struct {
+	name        string
+	description string
+	rootPath    string
+}
+
+// Name returns the provider name
+func (p *BaseProvider) Name() string {
+	return p.name
+}
+
+// Description returns the provider description
+func (p *BaseProvider) Description() string {
+	return p.description
+}
+
+// GetRootPath returns the root path for this provider
+func (p *BaseProvider) GetRootPath() string {
+	return p.rootPath
+}
+
+// IsRootPath checks if the given path is the root path for this provider
+func (p *BaseProvider) IsRootPath(path string) bool {
+	return normalizePath(path) == normalizePath(p.rootPath)
+}
+
+// ParsePath parses a path and returns the subpath relative to the provider root
+func (p *BaseProvider) ParsePath(path string) string {
+	normalized := normalizePath(path)
+	rootNormalized := normalizePath(p.rootPath)
+
+	if normalized == rootNormalized {
+		return ""
+	}
+
+	if len(normalized) > len(rootNormalized) && normalized[:len(rootNormalized)+1] == rootNormalized+"/" {
+		return normalized[len(rootNormalized)+1:]
+	}
+
+	return normalized
+}
+
+// SplitPath splits a path into components
+func SplitPath(path string) []string {
+	path = normalizePath(path)
+	if path == "" {
+		return []string{}
+	}
+	parts := splitString(path, '/')
+	result := make([]string, 0, len(parts))
+	for _, part := range parts {
+		if part != "" {
+			result = append(result, part)
+		}
+	}
+	return result
+}
+
+// normalizePath normalizes a path (removes leading/trailing slashes, handles "." and "..")
+func normalizePath(path string) string {
+	path = trimSpace(path)
+	if path == "" {
+		return ""
+	}
+
+	// Remove leading slashes
+	for len(path) > 0 && path[0] == '/' {
+		path = path[1:]
+	}
+
+	// Remove trailing slashes
+	for len(path) > 0 && path[len(path)-1] == '/' {
+		path = path[:len(path)-1]
+	}
+
+	// Handle "." and ".."
+	parts := splitString(path, '/')
+	result := make([]string, 0, len(parts))
+	for _, part := range parts {
+		switch part {
+		case "", ".":
+			// Skip empty and current directory
+			continue
+		case "..":
+			// Go up one directory
+			if len(result) > 0 {
+				result = result[:len(result)-1]
+			}
+		default:
+			result = append(result, part)
+		}
+	}
+
+	return joinStrings(result, "/")
+}
+
+// Helper functions to avoid importing strings package in basic operations
+func trimSpace(s string) string {
+	start := 0
+	end := len(s)
+	for start < end && (s[start] == ' ' || s[start] == '\t' || s[start] == '\n' || s[start] == '\r') {
+		start++
+	}
+	for end > start && (s[end-1] == ' ' || s[end-1] == '\t' || s[end-1] == '\n' || s[end-1] == '\r') {
+		end--
+	}
+	return s[start:end]
+}
+
+func splitString(s string, sep byte) []string {
+	var result []string
+	start := 0
+	for i := 0; i < len(s); i++ {
+		if s[i] == sep {
+			result = append(result, s[start:i])
+			start = i + 1
+		}
+	}
+	result = append(result, s[start:])
+	return result
+}
+
+func joinStrings(strs []string, sep string) string {
+	if len(strs) == 0 {
+		return ""
+	}
+	if len(strs) == 1 {
+		return strs[0]
+	}
+	result := strs[0]
+	for i := 1; i < len(strs); i++ {
+		result += sep + strs[i]
+	}
+	return result
+}