fix(docker): move dedup helper to a model-free module (CI green)

The widget-dedup test imported plugins.docker.routes, which re-imports
plugins.docker.models after the app already loaded the docker plugin —
"Table 'docker_containers' is already defined". Same plugin-loader gotcha the
host_agent query helpers avoid.

Extract dedup_by_container_id into plugins/docker/dedup.py (imports no ORM
models, so it's safe to import in either environment); routes.py imports it
from there and the test targets the model-free module.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016Jg27rgypiW2efULXJDtMC

plugins/docker/dedup.py

@@ -0,0 +1,27 @@
+"""Model-free Docker view helpers.
+
+Kept separate from routes.py/models.py so tests can import it directly: importing
+a module that re-imports plugins.docker.models AFTER the app has loaded the docker
+plugin raises "Table 'docker_containers' is already defined". This module touches
+no ORM models, so it's safe to import in either environment.
+"""
+from __future__ import annotations
+
+
+def dedup_by_container_id(containers: list) -> list:
+    """Collapse containers double-reported across hosts. Swarm-aware agents on
+    every manager list cluster-wide tasks, so the same container (identical
+    container_id) arrives once per manager and would otherwise be counted N times.
+    Keep the first occurrence per non-empty container_id — callers order
+    running-first, so a running report wins over a stale stopped one. Rows without
+    a container_id (older agents) can't be matched, so they're kept as-is."""
+    seen: set[str] = set()
+    out = []
+    for c in containers:
+        cid = (c.container_id or "").strip()
+        if cid:
+            if cid in seen:
+                continue
+            seen.add(cid)
+        out.append(c)
+    return out