[Security] HIGH-02 Validate hostname before it reaches shell commands

[kenken64]

Summary

Hostname is user-controlled and is interpolated into deploy command strings without strict validation.

Finding

• ID: HIGH-02
• Severity: High
• Source: docs/EVAL_SECURITY_FLAW.md

Affected Files

• crates/clawmacdo-cli/src/commands/deploy.rs
• crates/clawmacdo-cli/src/commands/serve.rs

Goal

Reject invalid hostnames before building deploy commands.

Likely Changes

• Add shared hostname validation.
• Apply validation at CLI entry points and any HTTP request boundary that accepts hostname.
• Return a clear validation error instead of proceeding.

Acceptance Criteria

• Hostnames are validated against a strict allowed pattern before use.
• Invalid hostnames are rejected with a user-facing error.
• Valid hostnames continue to work across Tencent, DigitalOcean, and Lightsail flows.
• No deploy command string includes unchecked hostname input.
• README usage docs mention hostname requirements if they are user-visible.