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>

src/coinhunter/config.py

@@ -17,7 +17,7 @@ except ModuleNotFoundError:  # pragma: no cover
 DEFAULT_CONFIG = """[runtime]
 timezone = "Asia/Shanghai"
 log_dir = "logs"
-output_format = "json"
+output_format = "tui"
 
 [binance]
 spot_base_url = "https://api.binance.com"