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/search/fts.py

@@ -0,0 +1,69 @@
+from __future__ import annotations
+
+import sqlite3
+from pathlib import Path
+
+
+class FTSEngine:
+    def __init__(self, db_path: str | Path) -> None:
+        self._conn = sqlite3.connect(str(db_path), check_same_thread=False)
+        self._conn.execute(
+            "CREATE VIRTUAL TABLE IF NOT EXISTS docs "
+            "USING fts5(content, tokenize='porter unicode61')"
+        )
+        self._conn.execute(
+            "CREATE TABLE IF NOT EXISTS docs_meta "
+            "(id INTEGER PRIMARY KEY, path TEXT)"
+        )
+        self._conn.commit()
+
+    def add_documents(self, docs: list[tuple[int, str, str]]) -> None:
+        """Add documents in batch. docs: list of (id, path, content)."""
+        if not docs:
+            return
+        self._conn.executemany(
+            "INSERT OR REPLACE INTO docs_meta (id, path) VALUES (?, ?)",
+            [(doc_id, path) for doc_id, path, content in docs],
+        )
+        self._conn.executemany(
+            "INSERT OR REPLACE INTO docs (rowid, content) VALUES (?, ?)",
+            [(doc_id, content) for doc_id, path, content in docs],
+        )
+        self._conn.commit()
+
+    def exact_search(self, query: str, top_k: int = 50) -> list[tuple[int, float]]:
+        """FTS5 MATCH query, return (id, bm25_score) sorted by score descending."""
+        try:
+            rows = self._conn.execute(
+                "SELECT rowid, bm25(docs) AS score FROM docs "
+                "WHERE docs MATCH ? ORDER BY score LIMIT ?",
+                (query, top_k),
+            ).fetchall()
+        except sqlite3.OperationalError:
+            return []
+        # bm25 in SQLite FTS5 returns negative values (lower = better match)
+        # Negate so higher is better
+        return [(int(row[0]), -float(row[1])) for row in rows]
+
+    def fuzzy_search(self, query: str, top_k: int = 50) -> list[tuple[int, float]]:
+        """Prefix search: each token + '*', return (id, score) sorted descending."""
+        tokens = query.strip().split()
+        if not tokens:
+            return []
+        prefix_query = " ".join(t + "*" for t in tokens)
+        try:
+            rows = self._conn.execute(
+                "SELECT rowid, bm25(docs) AS score FROM docs "
+                "WHERE docs MATCH ? ORDER BY score LIMIT ?",
+                (prefix_query, top_k),
+            ).fetchall()
+        except sqlite3.OperationalError:
+            return []
+        return [(int(row[0]), -float(row[1])) for row in rows]
+
+    def get_content(self, doc_id: int) -> str:
+        """Retrieve content for a doc_id."""
+        row = self._conn.execute(
+            "SELECT content FROM docs WHERE rowid = ?", (doc_id,)
+        ).fetchone()
+        return row[0] if row else ""