Add CPU sparkline to dashboard in compose mode

- New docker_stats.py module reads container stats from Docker socket
  using only asyncio + stdlib (no new dependencies)
- Calculates CPU % from delta of cpu_usage and system_cpu_usage
- Maintains ring buffer of last 30 CPU readings per container
- render_sparkline_svg() generates mini SVG chart from history
- DockerStatsCollector polls containers every 2 seconds
- New /cpu-sparkline.svg endpoint serves sparkline for a container
- Dashboard shows sparkline in tile header next to container name
- Only active in compose mode (--compose-manifest flag)
- Graceful degradation if Docker socket unavailable

Bump version to 0.1.17

src/textual_webterm/cli.py

@@ -149,10 +149,12 @@ def app(
     _config = default_config()
 
     landing_apps: list = []
+    is_compose_mode = False
     if landing_manifest:
         landing_apps = load_landing_yaml(landing_manifest)
     elif compose_manifest:
         landing_apps = load_compose_manifest(compose_manifest)
+        is_compose_mode = True
 
     server = LocalServer(
         "./",
@@ -160,6 +162,7 @@ def app(
         host=host,
         port=port,
         landing_apps=landing_apps,
+        compose_mode=is_compose_mode,
     )
     for app_entry in landing_apps:
         server.add_terminal(app_entry.name, app_entry.command, slug=app_entry.slug)