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/test_small_e2e.py

@@ -11,13 +11,13 @@ from pathlib import Path
 sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
 
 import numpy as np
-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.base import BaseReranker
-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.base import BaseReranker
+from codexlens_search.search.fts import FTSEngine
+from codexlens_search.search.pipeline import SearchPipeline
 
 
 class KeywordReranker(BaseReranker):
@@ -32,7 +32,7 @@ class KeywordReranker(BaseReranker):
         return scores
 
 PROJECT = Path(__file__).parent.parent
-TARGET_DIR = PROJECT / "src" / "codexlens"  # ~21 .py files, small
+TARGET_DIR = PROJECT / "src" / "codexlens_search"  # ~21 .py files, small
 INDEX_DIR = PROJECT / ".test_index_cache"
 EXTENSIONS = {".py"}