feat: shell completions (bash/zsh/fish/nushell) + VeriSimDB E2E test

- Add clap_complete + clap_complete_nushell for completion generation
- New 'completions' subcommand writes shell completions to stdout
- Pre-generated completions in completions/ directory
- Add just completions recipe
- Add tests/verisimdb_e2e.sh for REST gateway integration testing
- Add just e2e-verisimdb recipe

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

Author: hyperpolymath

Cargo.lock

@@ -11,6 +11,8 @@ repository = "https://github.com/hyperpolymath/panic-attacker"
 
 [dependencies]
 clap = { version = "4.5", features = ["derive"] }
+clap_complete = "4.5"
+clap_complete_nushell = "4.5"
 colored = "2.1"
 anyhow = "1.0"
 serde = { version = "1.0", features = ["derive"] }