fix(cli): validate selected local paths before resolution

Reuse the nonempty NUL-free local path contract before normalization in artifact commands, auxiliary inputs, and output destinations. Empty selections now fail at parsing instead of selecting the working directory; explicit relative paths preserve their target.

Public CLI checks cover primary and auxiliary empty paths, exact relative-file digest, explicit current-directory selection, symlink parent semantics, and environment export inputs. Correct the desktop fixture to assert the existing CLI validation envelope.

docs/cli.md

@@ -39,6 +39,11 @@ pass an absolute path. REA reads and authenticates the file, then projects it
 like retained Evidence, so a large file is bounded by the file reader rather
 than charged as inline input.
 
+Local file inspection commands reject empty paths and NUL bytes before resolving
+relative inputs, auxiliary files or output destinations. An empty string never
+selects the working directory; use an explicit `.` when selecting that directory
+is supported by the command.
+
 For example, a 334 MB Obsidian application Evidence file yields a summary view
 of about 10 KB. Replace the view with
 `{"kind": "page", "collection": "modules", "offset": 0, "limit": 32}` for a