feat(docker): container log viewer + Settings controls [M79 step 5]

The user-facing half (rule 27). Per-container log viewer + admin controls, so
container logs are something the operator can actually touch.

Viewer (plugins/docker):
- /container/<host>/<name>/logs full page + /logs/lines HTMX fragment polled
  every 5s (near-live follow); stream filter (all/stdout/stderr) + case-insensitive
  text search; newest-first so the latest lines survive the poll's scroll reset;
  empty/loading states; a "View logs" link from the container detail page.
  Jinja auto-escapes log content (no markup injection).

Settings (Thresholds & Retention tab):
- global on/off toggle, comma-separated exclude list, retention days + max MB
  per container — DB-backed, no restart. The toggle + exclude are enforced
  authoritatively at ingest (_persist_logs drops disabled/excluded lines), since
  the push model has no channel to tell an agent to stop.

Tests: route-defined smoke; template-parse covers the new templates; integration
test for the ingest-time toggle + exclude enforcement.

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

plugins/docker/routes.py

@@ -16,8 +16,8 @@ from steward.core.time_range import parse_range, DEFAULT_RANGE
 from .dedup import dedup_by_container_id
 from .swarm_view import build_swarm_services
 from .models import (
-    DockerContainer, DockerDiskUsage, DockerEvent, DockerImage, DockerMetric,
-    DockerSwarmNode, DockerSwarmService,
+    DockerContainer, DockerDiskUsage, DockerEvent, DockerImage, DockerLog,
+    DockerMetric, DockerSwarmNode, DockerSwarmService,
 )
 
 docker_bp = Blueprint("docker", __name__, template_folder="templates")
@@ -647,3 +647,56 @@ async def container_history(host_id: str, name: str):
         have_data=len(cpu_hist) >= 2,
         range_key=range_key,
     )
+
+
+# Newest lines returned per fetch — the retained window is bounded by the ring,
+# but a container can still hold thousands of lines; cap what one fetch renders.
+_LOG_TAIL_DEFAULT = 500
+
+
+async def _query_logs(db, host_id: str, name: str, stream: str, query: str,
+                      limit: int) -> list:
+    """The recent retained lines for one container, newest-first, optionally
+    filtered by stream and a case-insensitive substring.
+
+    Newest-first is deliberate: the viewer replaces the list on each poll, which
+    resets scroll to the top — so the latest lines stay visible without any
+    scroll handling, and older lines are a scroll away.
+    """
+    stmt = (select(DockerLog.ts, DockerLog.stream, DockerLog.line)
+            .where(DockerLog.host_id == host_id)
+            .where(DockerLog.container_name == name))
+    if stream in ("stdout", "stderr"):
+        stmt = stmt.where(DockerLog.stream == stream)
+    if query:
+        stmt = stmt.where(DockerLog.line.ilike(f"%{query}%"))
+    stmt = stmt.order_by(DockerLog.ts.desc(), DockerLog.id.desc()).limit(limit)
+    return (await db.execute(stmt)).all()
+
+
+@docker_bp.get("/container/<host_id>/<name>/logs")
+@require_role(UserRole.viewer)
+async def container_logs(host_id: str, name: str):
+    """Full log-viewer page for one container (lines load via an HTMX fragment)."""
+    async with current_app.db_sessionmaker() as db:
+        host = await db.get(Host, host_id)
+    return await render_template(
+        "docker/container_logs.html", host=host, host_id=host_id, name=name,
+    )
+
+
+@docker_bp.get("/container/<host_id>/<name>/logs/lines")
+@require_role(UserRole.viewer)
+async def container_logs_lines(host_id: str, name: str):
+    """HTMX fragment: the recent retained log lines, stream + text filtered.
+    Polled every few seconds by the viewer for near-live follow."""
+    stream = request.args.get("stream", "all")
+    query = (request.args.get("q") or "").strip()
+    async with current_app.db_sessionmaker() as db:
+        rows = await _query_logs(db, host_id, name, stream, query, _LOG_TAIL_DEFAULT)
+    return await render_template(
+        "docker/_container_logs_lines.html",
+        lines=[{"ts": r.ts, "stream": r.stream, "line": r.line} for r in rows],
+        name=name, tail=_LOG_TAIL_DEFAULT,
+        filtered=bool(query) or stream in ("stdout", "stderr"),
+    )