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>

README.md

@@ -53,6 +53,8 @@ This creates:
 - `~/.coinhunter/.env`
 - `~/.coinhunter/logs/`
 
+If you are using **zsh** or **bash**, `init` will also generate and install shell completion scripts automatically, and update your rc file (`~/.zshrc` or `~/.bashrc`) if needed.
+
 `config.toml` stores runtime and strategy settings. `.env` stores:
 
 ```bash
@@ -93,6 +95,10 @@ coinhunter opportunity scan --symbols BTCUSDT ETHUSDT SOLUSDT
 
 # Self-upgrade
 coinhunter upgrade
+
+# Shell completion (manual)
+coinhunter completion zsh  > ~/.zsh/completions/_coinhunter
+coinhunter completion bash > ~/.local/share/bash-completion/completions/coinhunter
 ```
 
 `upgrade` will try `pipx upgrade coinhunter` first, and fall back to `pip install --upgrade coinhunter` if pipx is not available.