feat: add CopyButton component and copy-to-clipboard across dashboard

New reusable CopyButton component with checkmark feedback after copy.

Added copy buttons to:
- SSH public key display (add repo modal)
- Webhook URL field (edit repo modal)
- Webhook secret field (edit repo modal)
- Code snippets in finding detail (via enhanced CodeSnippet component)
- Suggested fix code blocks
- MCP server endpoint URLs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

compliance-dashboard/src/components/mod.rs

@@ -2,6 +2,7 @@ pub mod app_shell;
 pub mod attack_chain;
 pub mod code_inspector;
 pub mod code_snippet;
+pub mod copy_button;
 pub mod file_tree;
 pub mod help_chat;
 pub mod notification_bell;