refactor: 移除图索引功能，修复内存泄露，优化嵌入生成

主要更改:

1. 移除图索引功能 (graph indexing)
   - 删除 graph_analyzer.py 及相关迁移文件
   - 移除 CLI 的 graph 命令和 --enrich 标志
   - 清理 chain_search.py 中的图查询方法 (370行)
   - 删除相关测试文件

2. 修复嵌入生成内存问题
   - 重构 generate_embeddings.py 使用流式批处理
   - 改用 embedding_manager 的内存安全实现
   - 文件从 548 行精简到 259 行 (52.7% 减少)

3. 修复内存泄露
   - chain_search.py: quick_search 使用 with 语句管理 ChainSearchEngine
   - embedding_manager.py: 使用 with 语句管理 VectorStore
   - vector_store.py: 添加暴力搜索内存警告

4. 代码清理
   - 移除 Symbol 模型的 token_count 和 symbol_type 字段
   - 清理相关测试用例

测试: 760 passed, 7 skipped

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

codex-lens/src/codexlens/storage/index_tree.py

@@ -16,7 +16,6 @@ from typing import Dict, List, Optional, Set
 
 from codexlens.config import Config
 from codexlens.parsers.factory import ParserFactory
-from codexlens.semantic.graph_analyzer import GraphAnalyzer
 from codexlens.storage.dir_index import DirIndexStore
 from codexlens.storage.path_mapper import PathMapper
 from codexlens.storage.registry import ProjectInfo, RegistryStore
@@ -525,16 +524,6 @@ class IndexTreeBuilder:
                         symbols=indexed_file.symbols,
                     )
 
-                    # Extract and store code relationships for graph visualization
-                    if language_id in {"python", "javascript", "typescript"}:
-                        graph_analyzer = GraphAnalyzer(language_id)
-                        if graph_analyzer.is_available():
-                            relationships = graph_analyzer.analyze_with_symbols(
-                                text, file_path, indexed_file.symbols
-                            )
-                            if relationships:
-                                store.add_relationships(file_path, relationships)
-
                     files_count += 1
                     symbols_count += len(indexed_file.symbols)
 
@@ -742,16 +731,6 @@ def _build_dir_worker(args: tuple) -> DirBuildResult:
                     symbols=indexed_file.symbols,
                 )
 
-                # Extract and store code relationships for graph visualization
-                if language_id in {"python", "javascript", "typescript"}:
-                    graph_analyzer = GraphAnalyzer(language_id)
-                    if graph_analyzer.is_available():
-                        relationships = graph_analyzer.analyze_with_symbols(
-                            text, item, indexed_file.symbols
-                        )
-                        if relationships:
-                            store.add_relationships(item, relationships)
-
                 files_count += 1
                 symbols_count += len(indexed_file.symbols)