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/src/codexlens_search/rerank/local.py

@@ -0,0 +1,25 @@
+from __future__ import annotations
+
+from codexlens_search.config import Config
+from .base import BaseReranker
+
+
+class FastEmbedReranker(BaseReranker):
+    """Local reranker backed by fastembed TextCrossEncoder."""
+
+    def __init__(self, config: Config) -> None:
+        self._config = config
+        self._model = None
+
+    def _load(self) -> None:
+        if self._model is None:
+            from fastembed.rerank.cross_encoder import TextCrossEncoder
+            self._model = TextCrossEncoder(model_name=self._config.reranker_model)
+
+    def score_pairs(self, query: str, documents: list[str]) -> list[float]:
+        self._load()
+        results = list(self._model.rerank(query, documents))
+        scores = [0.0] * len(documents)
+        for r in results:
+            scores[r.index] = float(r.score)
+        return scores