fix(docker): a container's memory is its processes' own; file cache shown on its page (#6030)

The agent sent Docker's working set (usage less inactive_file), which still
counts recently used file cache. A file-heavy container with no limit read
191 GB while its processes held 2.2 GB, and the host's own figure, which
already leaves cache out, disagreed with it.

Agent 1.23.0 sends mem_used_bytes / mem_used_pct (anon + shmem, so
Postgres's shared buffers count; v1: rss + shmem) and mem_cache_bytes
apart. The new names keep the two meanings apart in history and in learned
normals: docker_013 renames the columns, clears the old values and adds
mem_cache_bytes. The Docker page, swarm by-node sums, Busiest Containers,
container detail, normals and the MCP tools all read the new figure. File
cache is shown only on the container's page and in get_container.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/core/test_norm_grading.py

@@ -101,7 +101,7 @@ def test_a_monitor_down_stays_down_whatever_its_normal():
 
 def test_a_containers_cpu_is_learned_per_core_and_said_in_cores():
     # 3.8 cores of a 4-core host is 95% of it: crit, unless 3.6 cores is usual.
-    c = NS(cpu_pct=380.0, mem_pct=50.0, mem_usage_bytes=2**30, mem_limit_bytes=2 * 2**30)
+    c = NS(cpu_pct=380.0, mem_used_pct=50.0, mem_used_bytes=2**30, mem_limit_bytes=2 * 2**30)
     u = usage(c, 4, 64 * 2**30, thresholds=TH, norms={"cpu_pct": _norm(360.0)})
     assert u["cpu_grade"] == "ok" and u["cpu_usual"] == "usual 3.60 cores at this hour"
     assert usage(c, 4, 64 * 2**30, thresholds=TH)["cpu_grade"] == "crit"
@@ -109,8 +109,8 @@ def test_a_containers_cpu_is_learned_per_core_and_said_in_cores():
 
 
 def test_a_containers_memory_within_its_normal_reads_healthy():
-    c = NS(cpu_pct=1.0, mem_pct=92.0, mem_usage_bytes=2**30, mem_limit_bytes=2 * 2**30)
-    u = usage(c, 4, 64 * 2**30, thresholds=TH, norms={"mem_pct": _norm(90.0)})
+    c = NS(cpu_pct=1.0, mem_used_pct=92.0, mem_used_bytes=2**30, mem_limit_bytes=2 * 2**30)
+    u = usage(c, 4, 64 * 2**30, thresholds=TH, norms={"mem_used_pct": _norm(90.0)})
     assert (u["mem_grade"], u["mem_usual"]) == ("ok", "usual 90.0% at this hour")
     assert usage(c, 4, 64 * 2**30, thresholds=TH)["mem_grade"] == "crit"