feat: add Braille spinner, shell completions, and TUI polish

- Add with_spinner context manager with cyan Braille animation for human mode.
- Wrap all query/execution commands in cli.py with loading spinners.
- Integrate shtab: auto-install shell completions during init for zsh/bash.
- Add `completion` subcommand for manual script generation.
- Fix stale output_format default in DEFAULT_CONFIG (json → tui).
- Add help descriptions to all second-level subcommands.
- Version 2.0.4.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pyproject.toml

@@ -12,6 +12,7 @@ requires-python = ">=3.10"
 dependencies = [
   "binance-connector>=3.9.0",
   "binance-futures-connector>=4.1.0",
+  "shtab>=1.7.0",
   "tomli>=2.0.1; python_version < '3.11'",
 ]
 authors = [