feat: flatten opportunity commands, add config management, fix completions

- Flatten opportunity into top-level portfolio and opportunity commands
- Add interactive config get/set/key/secret with type coercion
- Rewrite --doc to show TUI vs JSON schema per command
- Unify agent mode output to JSON only
- Make init prompt for API key/secret interactively
- Fix coin tab completion alias binding
- Fix set_config_value reading from wrong path
- Fail loudly on invalid numeric config values

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -61,6 +61,8 @@ This creates:
 
 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.
 
+`init` interactively prompts for your Binance API key and secret if they are missing. Use `--no-prompt` to skip this.
+
 `config.toml` stores runtime and strategy settings. `.env` stores:
 
 ```bash
@@ -101,18 +103,32 @@ coinhunter sell BTCUSDT --qty 0.01 --type limit --price 90000
 coin b BTCUSDT -Q 100 -d
 coin s BTCUSDT -q 0.01 -t limit -p 90000
 
-# Opportunities (aliases: opp, o)
-coinhunter opportunity portfolio
-coinhunter opportunity scan
-coinhunter opportunity scan --symbols BTCUSDT ETHUSDT SOLUSDT
-coin opp pf
-coin o scan -s BTCUSDT ETHUSDT
+# Portfolio (aliases: pf, p)
+coinhunter portfolio
+coinhunter portfolio --agent
+coin pf
+
+# Opportunity scanning (aliases: o)
+coinhunter opportunity
+coinhunter opportunity --symbols BTCUSDT ETHUSDT SOLUSDT
+coin o -s BTCUSDT ETHUSDT
 
 # Audit log
 coinhunter catlog
 coinhunter catlog -n 20
 coinhunter catlog -n 10 -o 10
 
+# Configuration management (aliases: cfg, c)
+coinhunter config get                    # show all config
+coinhunter config get binance.recv_window
+coinhunter config set opportunity.top_n 20
+coinhunter config set trading.dry_run_default true
+coinhunter config set market.universe_allowlist BTCUSDT,ETHUSDT
+coinhunter config key YOUR_API_KEY       # or omit value to prompt interactively
+coinhunter config secret YOUR_SECRET     # or omit value to prompt interactively
+coin c get opportunity.top_n
+coin c set trading.dry_run_default false
+
 # Self-upgrade
 coinhunter upgrade
 coin upgrade