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/api/tests/test_ssh_keys_api.py

@@ -0,0 +1,22 @@
+import pytest
+from httpx import AsyncClient
+
+from src.main import app
+
+
+@pytest.fixture
+async def async_client():
+    async with AsyncClient(app=app, base_url="http://test") as client:
+        yield client
+
+
+@pytest.mark.asyncio
+async def test_create_ssh_key_requires_authentication(async_client: AsyncClient) -> None:
+    response = await async_client.post("/ssh-keys", json={"name": "test-key"})
+    assert response.status_code == 401
+
+
+@pytest.mark.asyncio
+async def test_list_ssh_keys_requires_authentication(async_client: AsyncClient) -> None:
+    response = await async_client.get("/ssh-keys")
+    assert response.status_code == 401