feat(docker): persist pushed container logs into docker_logs [M79 step 3]

Ingest side of container logs. The host_agent ingest route extracts
sample["docker_logs"] as time-series batches (append every line, each carrying
its own Docker ts with recorded_at as fallback) and hands them to the docker
capability alongside the existing container/swarm/disk data — still under the
begin_nested SAVEPOINT so a logs failure can't sink host metrics.

- ingest.py: _persist_logs + pure _log_rows(batches, host_id) that shapes/filters
  records (drops the _steward truncation marker, malformed + lineless records,
  normalises unknown stream → stdout); persist_host_docker gains a logs= param
- routes.py: accumulate docker_log_batches, add to the guard + capability call
- unit test for _log_rows shaping/filtering; integration push→store→query test

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CAGR73DUowdVFVvYzLXC5C

tests/integration/test_docker.py

@@ -172,6 +172,44 @@ def test_persist_scopes_containers_by_host(app):
     assert enrich == ("healthy", 2, "web", 1000)   # enrichment round-trips
 
 
+@_NEEDS_DB
+def test_persist_logs_stores_lines(app):
+    """Pushed container logs land in docker_logs, host-scoped, one row per line,
+    ordered by their own ts; the agent's _steward truncation marker is dropped."""
+    from sqlalchemy import text
+    from steward.models.hosts import Host
+
+    persist = _persist_fn(app)
+    now = datetime.now(timezone.utc)
+    log_batches = [(now, [
+        {"container": "web", "stream": "stdout",
+         "ts": "2026-01-01T00:00:01+00:00", "line": "started"},
+        {"container": "web", "stream": "stderr",
+         "ts": "2026-01-01T00:00:02+00:00", "line": "warn: x"},
+        {"container": "_steward", "stream": "stderr", "ts": None, "line": "truncated"},
+    ])]
+
+    async def _go():
+        async with app.db_sessionmaker() as s:
+            async with s.begin():
+                await s.execute(text("DELETE FROM docker_logs"))
+                h = Host(id=str(uuid.uuid4()), name="loghost", address="10.0.0.9")
+                s.add(h)
+                await s.flush()
+                hid = h.id
+                # snapshots empty; logs passed as the 6th positional arg.
+                await persist(s, h, [], None, None, log_batches)
+            rows = (await s.execute(text(
+                "SELECT container_name, stream, line FROM docker_logs "
+                "WHERE host_id = :h ORDER BY ts"), {"h": hid})).all()
+            return [tuple(r) for r in rows]
+
+    assert asyncio.run(_go()) == [
+        ("web", "stdout", "started"),
+        ("web", "stderr", "warn: x"),
+    ]
+
+
 @_NEEDS_DB
 def test_large_memory_values_persist_as_bigint(app):
     """A container using >2^31 bytes of RAM must persist. Regression: mem_usage_bytes