feat(codex-lens): add unified reranker architecture and file watcher

Unified Reranker Architecture:
- Add BaseReranker ABC with factory pattern
- Implement 4 backends: ONNX (default), API, LiteLLM, Legacy
- Add .env configuration parsing for API credentials
- Migrate from sentence-transformers to optimum+onnxruntime

File Watcher Module:
- Add real-time file system monitoring with watchdog
- Implement IncrementalIndexer for single-file updates
- Add WatcherManager with signal handling and graceful shutdown
- Add 'codexlens watch' CLI command
- Event filtering, debouncing, and deduplication
- Thread-safe design with proper resource cleanup

Tests: 16 watcher tests + 5 reranker test files

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

codex-lens/pyproject.toml

@@ -21,6 +21,7 @@ dependencies = [
     "tree-sitter-javascript>=0.25",
     "tree-sitter-typescript>=0.23",
     "pathspec>=0.11",
+    "watchdog>=3.0",
 ]
 
 [project.optional-dependencies]
@@ -50,11 +51,35 @@ semantic-directml = [
 ]
 
 # Cross-encoder reranking (second-stage, optional)
-# Install with: pip install codexlens[reranker]
-reranker = [
+# Install with: pip install codexlens[reranker] (default: ONNX backend)
+reranker-onnx = [
+    "optimum>=1.16",
+    "onnxruntime>=1.15",
+    "transformers>=4.36",
+]
+
+# Remote reranking via HTTP API
+reranker-api = [
+    "httpx>=0.25",
+]
+
+# LLM-based reranking via ccw-litellm
+reranker-litellm = [
+    "ccw-litellm>=0.1",
+]
+
+# Legacy sentence-transformers CrossEncoder reranker
+reranker-legacy = [
     "sentence-transformers>=2.2",
 ]
 
+# Backward-compatible alias for default reranker backend
+reranker = [
+    "optimum>=1.16",
+    "onnxruntime>=1.15",
+    "transformers>=4.36",
+]
+
 # Encoding detection for non-UTF8 files
 encoding = [
     "chardet>=5.0",