refactor: modularize CLI and optimize cache metadata lookups

- Extract error handling, path validation, and handlers into separate modules
- Add CacheCheckResult to pre-fetch metadata and avoid double lookups
- Deprecate legacy cache methods in favor of optimized alternatives
- Enable tokio fs feature for async file operations
- Remove debug profile from release build

src/cli/path_utils.rs

@@ -0,0 +1,30 @@
+use std::path::{Path, PathBuf};
+
+/// Validates that a path exists and is a readable directory.
+/// Returns the canonicalized path if validation succeeds.
+pub async fn validate_and_normalize_path(path: &Path) -> Result<PathBuf, String> {
+    // Use tokio::fs for async file operations
+    let metadata = tokio::fs::metadata(path).await.map_err(|e| {
+        if e.kind() == std::io::ErrorKind::NotFound {
+            format!("Path '{}' does not exist", path.display())
+        } else {
+            format!("Cannot access '{}': {}", path.display(), e)
+        }
+    })?;
+
+    if !metadata.is_dir() {
+        return Err(format!("Path '{}' is not a directory", path.display()));
+    }
+
+    // Check if we can read the directory
+    let _ = tokio::fs::read_dir(path)
+        .await
+        .map_err(|e| format!("Cannot access directory '{}': {}", path.display(), e))?;
+
+    // canonicalize is sync-only, use spawn_blocking
+    let path_owned = path.to_path_buf();
+    tokio::task::spawn_blocking(move || path_owned.canonicalize())
+        .await
+        .map_err(|e| format!("Task failed: {}", e))?
+        .map_err(|e| format!("Failed to normalize path '{}': {}", path.display(), e))
+}