feat(services): sleep mode — scale-to-zero on idle, wake on traffic

Services gain sleep_enabled + sleep_idle_minutes. A 30s sweeper tracks
container NetworkIO deltas; a flat counter for the configured window
scales the service to zero (status=sleeping, workload containers removed).

While slept, a busybox wake container takes over the service's Traefik
host rule at priority 100: it serves a self-reloading "waking" page and
calls the unauthenticated idempotent GET/POST /api/v1/internal/wake/:id,
which reconciles the service back to running. Wake placeholders carry a
dedicated label (containr.wake-for) so runtime state never counts them;
the sweeper prunes them once the workload is up. The wake URL resolves
the API via its container name when containerized, else the edge
network's IPAM gateway — bare-metal installs need HOST=0.0.0.0 for the
callback.

Surfaces: PUT fields on services, POST /services/:id/sleep|wake,
CLI --sleep/--sleep-idle + services sleep|wake, 2 MCP tools (89 total),
OpenAPI paths/schema, and a Settings > Sleep card with toggle, idle
minutes, and manual sleep/wake plus a Sleeping badge.

Verified live: idle sweep scaled whoami-web to zero; the wake container
served the page on the edge network and its callback woke the service
(container recreated, status running, placeholder pruned).

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/docker/client.go

@@ -371,6 +371,21 @@ func (c *Client) RemoveNetwork(ctx context.Context, networkID string) error {
 	return c.cli.NetworkRemove(ctx, networkID)
 }
 
+// NetworkGateway returns the IPAM gateway of a network — the address
+// containers on it can use to reach host-published ports.
+func (c *Client) NetworkGateway(ctx context.Context, networkID string) string {
+	resp, err := c.cli.NetworkInspect(ctx, networkID, network.InspectOptions{})
+	if err != nil {
+		return ""
+	}
+	for _, cfg := range resp.IPAM.Config {
+		if cfg.Gateway != "" {
+			return cfg.Gateway
+		}
+	}
+	return ""
+}
+
 // ConnectNetwork connects a container to a network
 func (c *Client) ConnectNetwork(ctx context.Context, networkID, containerID string, config network.EndpointSettings) error {
 	return c.cli.NetworkConnect(ctx, networkID, containerID, &config)