doc-linter: narrow argv parsing exception scope to (IndexError, SyntaxError, ValueError)

CodeRabbit / Ruff BLE001: the previous 'except Exception as e:' on the
explicit-file-list path caught any error, masking runtime failures
from handle_file_action() as silent fallback behavior. Only input
validation errors from ast.literal_eval(sys.argv[1]) should trigger
the fallback walk.

Refactor:

- Wrap only the parse step in try/except, catching just IndexError
  (missing argv[1]), SyntaxError (malformed literal), and ValueError
  (non-literal input).
- On parse failure, set files = None and dispatch to the DOCS_ROOT
  walk via an explicit 'else' branch.
- On parse success, run the file loop outside the try so any errors
  from handle_file_action() propagate normally and CI fails loudly.

Also drops the unused 'as e' (Ruff BLE001 noise) and the implicit
catch of TypeError (e.g. ast.literal_eval('42') returns an int and
'for file in 42:' would have been silently swallowed -> fallback
walk; now it raises clearly).

Verified scenarios:
- explicit file list (CI normal path) -> exit 0.
- no argv -> IndexError caught -> walks DOCS_ROOT.
- malformed argv ('not-a-list') -> SyntaxError caught -> walks DOCS_ROOT.
- explicit list with a non-existent file -> FileNotFoundError
  propagates (previously silently triggered a fallback walk).
- explicit list with a non-list literal ('42') -> TypeError
  propagates (programming error stays visible).

0 files changed, 0 insertions, 0 deletions