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/pyproject.toml

@@ -3,9 +3,9 @@ requires = ["hatchling"]
 build-backend = "hatchling.build"
 
 [project]
-name = "codex-lens-v2"
-version = "0.1.0"
-description = "Minimal code semantic search library with 2-stage pipeline"
+name = "codexlens-search"
+version = "0.2.0"
+description = "Lightweight semantic code search engine — 2-stage vector + FTS + RRF fusion"
 requires-python = ">=3.10"
 dependencies = []
 
@@ -33,4 +33,4 @@ dev = [
 ]
 
 [tool.hatch.build.targets.wheel]
-packages = ["src/codexlens"]
+packages = ["src/codexlens_search"]