Phase 15: dashboard stack resource usage (0.16.0)

The dashboard now lists stacks in a table with live CPU and memory usage per
stack. Usage is sampled from docker stats (one-shot read per running container,
using the daemon-provided precpu for the CPU delta) and aggregated by compose
project.

- services/stats_service.py + GET /api/stacks/stats: per-stack cpu_used (cores),
  mem_used (bytes minus reclaimable cache), and the summed assigned cpu/mem
  limits (null when none set), read concurrently across containers.
- Dashboard: stacks render as a table with a CPU and a Memory meter. When a
  limit is assigned the bar fills toward it (used / limit + %); otherwise it
  fills toward the host total. Inline start/stop/restart per row for admins.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -8,7 +8,8 @@ as intuitive as Dockge, as capable as Portainer for Compose workflows.
 > destinations) + Phase 7 (Scheduled backups) + Phase 8 (Remote-stack backups)
 > + Phase 9 (Networks) + Phase 10 (iGPU passthrough) + Phase 11 (Remote UX &
 > network attach) + Phase 12 (File browser) + Phase 13 (Multi-host networks &
-> images) + Phase 14 (Multi-host file browser) complete.
+> images) + Phase 14 (Multi-host file browser) + Phase 15 (Dashboard stack
+> resource usage) complete.
 
 ## What works today (Phase 1)
 
@@ -146,6 +147,16 @@ as intuitive as Dockge, as capable as Portainer for Compose workflows.
   container or connect any container on the host (`POST /api/networks/{id}/connect`
   / `/disconnect`).
 
+### Phase 15 — Dashboard stack resource usage
+
+- **The dashboard now lists stacks in a table** (status, services) with live
+  **CPU** and **memory** usage per stack, sampled from `docker stats` and
+  aggregated by compose project.
+- When a stack has `deploy.resources.limits` assigned, the bar fills toward that
+  limit and shows usage vs the limit (e.g. `0.42 / 1 cores`, `310 MB / 512 MB`);
+  otherwise it shows absolute usage against the host total. Inline start/stop/
+  restart actions per row for admins. New endpoint `GET /api/stacks/stats`.
+
 ### Phase 14 — Multi-host file browser
 
 - **The Files page now has a host switcher.** When agents are registered, a