mciasctl: convert from flag to cobra

Adds shell completion support (zsh, bash, fish) via cobra's built-in
completion command. All existing behavior and security measures are
preserved.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/spf13/pflag/.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+indent_size = 4
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.go]
+indent_style = tab