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/assets/main.css

@@ -3877,3 +3877,15 @@ tbody tr:last-child td {
 .notification-item-pkg { font-size: 12px; color: var(--text-primary); font-family: 'JetBrains Mono', monospace; }
 .notification-item-repo { font-size: 11px; color: var(--text-secondary); margin-bottom: 4px; }
 .notification-item-summary { font-size: 11px; color: var(--text-secondary); line-height: 1.4; display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden; }
+
+/* ═══════════════════════════════════════════════════════════════
+   COPY BUTTON — Reusable clipboard copy component
+   ═══════════════════════════════════════════════════════════════ */
+.copy-btn { background: none; border: 1px solid var(--border); border-radius: 6px; padding: 5px 7px; color: var(--text-secondary); cursor: pointer; display: inline-flex; align-items: center; transition: color 0.15s, border-color 0.15s, background 0.15s; flex-shrink: 0; }
+.copy-btn:hover { color: var(--accent); border-color: var(--accent); background: var(--accent-muted); }
+.copy-btn-sm { padding: 3px 5px; border-radius: 4px; }
+/* Copyable inline field pattern: value + copy button side by side */
+.copyable { display: flex; align-items: center; gap: 6px; }
+.copyable code, .copyable .mono { flex: 1; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.code-snippet-wrapper { position: relative; }
+.code-snippet-header { display: flex; align-items: center; justify-content: space-between; margin-bottom: 4px; gap: 8px; }