fix(monitoring): dedupe container metrics by task suffix, not name prefix

[sensorialsn]

Problem

In the monitoring service, collectMetrics deduplicates the docker stats output by GetServiceName, which strips the last --separated segment of the container name:

parts := strings.Split(name, "-")
return strings.Join(parts[:len(parts)-1], "-")

Any set of containers sharing a dash prefix therefore collapses to a single deduplication key. With explicit compose container_names such as:

app-1425-app, app-1425-mysql, app-1425-redis, app-1425-queue

all four map to the key app-1425, so only the first container returned by docker stats is stored on each tick — the metrics of every sibling container are silently dropped, and which container "wins" depends on docker stats output order.

This is inconsistent with the storage and query layers, which are already keyed by the full container name:

• SaveContainerMetric stores metric.Name (full name) in container_metrics.container_name;
• GetLastNContainerMetrics filters with WHERE container_name = ? OR container_name LIKE ?||'.%'.

So the write-side dedup is the only place losing data.

Fix

Deduplicate by the swarm task prefix (the name up to the first .) instead of the last dash segment:

• swarm replicas myapp.1.taskid / myapp.2.taskid still collapse to myapp — the original intent (one stored series per service and tick) is preserved, and reads keep matching through the existing LIKE name||'.%' clause;
• compose containers (app-1425-mysql, project-web-1), which have no task suffix and are unique per container, keep distinct keys and are all stored.

Added a table-driven unit test for GetServiceName covering swarm replicas, explicit compose names, compose default naming, and the leading-slash case.

How to reproduce

1. Enable container monitoring with services whose container names share a dash prefix (e.g. a compose stack with container_name: mystack-app, mystack-mysql, mystack-redis).
2. Let the agent collect a few ticks.
3. Query GET /metrics/containers?appName=mystack-mysql&limit=50 — empty (or nearly empty) results, while mystack-app (or whichever container docker stats lists first) has all the points.

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