fix: prevent Dozzle from attempting to update its own container

[amir20]

Summary

• Detect when Dozzle is trying to update its own standalone container (amir20/dozzle image)
• Return an error with message to restart manually, since the image was already pulled
• Swarm services are unaffected — the swarm orchestrator handles restarts externally

Test plan

• Try updating Dozzle's own container in standalone mode — should get error message
• Try updating Dozzle as a swarm service — should work as before
• Try updating other standalone containers — should work as before

🤖 Generated with Claude Code

[claude]

• Bug: c.Image == "amir20/dozzle" won't match the most common usage — users typically run amir20/dozzle:latest or via GHCR (ghcr.io/amir20/dozzle). Consider strings.Contains(imageName, "amir20/dozzle") using the already-resolved imageName variable instead of c.Image.

• Minor: imageName (from inspectResp.Config.Image) is already available in scope and is the authoritative resolved image — prefer it over c.Image for the check for consistency.

[claude]

• strings.Contains(c.Image, "amir20/dozzle") could false-positive on images like myregistry.com/amir20/dozzle-fork. The original explicit check was safer; consider restoring c.Image == "amir20/dozzle" || strings.HasPrefix(c.Image, "amir20/dozzle:") and applying the same pattern in docker_service.go.
• docker_service.go: Sending an error progress event and then returning an error may double-report the error to the frontend — verify UI handles this correctly.
• No tests for the self-update guard path in UpdateContainer.