Phase 20: per-container inspect + start/stop/restart, local + agent (0.26.0)

Stack Overview now renders each service as an expandable ContainerCard with a
curated single-container inspect view and admin start/stop/restart buttons,
both for local stacks (GET/POST /api/containers/{id}[/{action}]) and remote
stacks (proxied via /api/agents/{id}/containers/* to the agent's new
/agent/containers/* endpoints). Only compose-managed containers are exposed.

Also bumps version 0.23.0 -> 0.26.0 (the bumps for the already-committed
Phase 18 image-prune / Phase 19 compose-validate were missed) and backfills
README sections for Phase 18/19/20.

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

backend/agent_app.py

@@ -40,6 +40,7 @@ from docker_client import DockerError, get_client, safe_call
 from services import (
     backup_service,
     compose_service,
+    container_service,
     device_service,
     file_service,
     image_service,
@@ -62,7 +63,7 @@ def _map_docker(exc: DockerError):
         raise HTTPException(status_code=code, detail=exc.detail or exc.error)
     raise exc  # falls through to the global 502 DockerError handler
 
-AGENT_VERSION = "0.23.0"
+AGENT_VERSION = "0.26.0"
 
 
 # --------------------------------------------------------------------------- #
@@ -504,6 +505,21 @@ def image_prune(all_unused: bool = Query(False, alias="all")) -> dict:
     return image_service.prune_images(all_unused)
 
 
+# --------------------------------------------------------------------------- #
+# Containers (single-container inspect + lifecycle)
+# --------------------------------------------------------------------------- #
+
+
+@app.get("/agent/containers/{container_id}", dependencies=[Depends(verify_token)])
+def inspect_container(container_id: str) -> dict:
+    return container_service.inspect_container(container_id)
+
+
+@app.post("/agent/containers/{container_id}/{action}", dependencies=[Depends(verify_token)])
+def container_action(container_id: str, action: str) -> dict:
+    return container_service.container_action(container_id, action)
+
+
 # --------------------------------------------------------------------------- #
 # Volumes
 # --------------------------------------------------------------------------- #