refactor: rename package codexlens -> codexlens_search for independent distribution

Rename the v2 search engine package to `codexlens-search` (import as
`codexlens_search`) so it can be installed independently and consumed
by the original codex-lens as a dependency. This avoids package path
conflicts since both previously used `src/codexlens/`.

Changes:
- Rename src/codexlens/ -> src/codexlens_search/
- Update pyproject.toml: name=codexlens-search, version=0.2.0
- Update all imports across source, tests, and scripts
- Add public API exports in __init__.py (Config, SearchPipeline,
  IndexingPipeline, SearchResult, IndexStats)

37/37 tests pass. No functional changes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

codex-lens-v2/scripts/index_and_search.py

@@ -9,13 +9,13 @@ from pathlib import Path
 # 确保 src 可被导入
 sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
 
-from codexlens.config import Config
-from codexlens.core.factory import create_ann_index, create_binary_index
-from codexlens.embed.local import FastEmbedEmbedder
-from codexlens.indexing import IndexingPipeline
-from codexlens.rerank.local import FastEmbedReranker
-from codexlens.search.fts import FTSEngine
-from codexlens.search.pipeline import SearchPipeline
+from codexlens_search.config import Config
+from codexlens_search.core.factory import create_ann_index, create_binary_index
+from codexlens_search.embed.local import FastEmbedEmbedder
+from codexlens_search.indexing import IndexingPipeline
+from codexlens_search.rerank.local import FastEmbedReranker
+from codexlens_search.search.fts import FTSEngine
+from codexlens_search.search.pipeline import SearchPipeline
 
 # ─── 配置 ──────────────────────────────────────────────────────────────────
 REPO_ROOT = Path("D:/Claude_dms3")