feat: implement SSH key management

- Add backend API endpoints for SSH key CRUD (POST, GET, DELETE)
- Implement Ed25519 key generation with Fernet-encrypted private keys
- Add frontend SSH keys page with generate, list, and delete functionality
- Include copy-to-clipboard for public keys
- Add responsive CSS styles for key cards
- Register ssh_keys router in main.py
- Add basic auth tests for SSH key endpoints

Quality gates: ruff ✓, mypy ✓, typecheck ✓, lint ✓

apps/web/src/styles.css

@@ -270,6 +270,69 @@ a {
   gap: 0.6rem;
 }
 
+.keys-list {
+  display: flex;
+  flex-direction: column;
+  gap: 0.75rem;
+}
+
+.key-card {
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: 14px;
+  padding: 1rem;
+}
+
+.key-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: 0.5rem;
+}
+
+.key-header h3 {
+  margin: 0;
+}
+
+.key-meta {
+  margin-bottom: 0.75rem;
+}
+
+.key-public {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  padding: 0.5rem;
+  background: #f5f3ee;
+  border-radius: 8px;
+}
+
+.key-public code {
+  font-size: 0.85rem;
+  word-break: break-all;
+  flex: 1;
+}
+
+.form-group {
+  display: flex;
+  flex-direction: column;
+  gap: 0.35rem;
+}
+
+.form-group input {
+  padding: 0.55rem 0.7rem;
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  font: inherit;
+}
+
+.error {
+  color: #b91c1c;
+  padding: 0.75rem;
+  background: #fef2f2;
+  border-radius: 10px;
+}
+
 @media (max-width: 860px) {
   .shell-body {
     grid-template-columns: 1fr;