feat(auth): share links open only their own widgets; unmarked routes are closed (#5033)

#5033 "Share links open only their own dashboard; every route without a
role is on an explicit allow-list". Any live share token in ?s= made the
caller a viewer on every viewer route — host pages, container logs, any
dashboard — and the host-agent widget routes had no role check at all.

- steward/dashboard/share.py: a share token opens, read-only, exactly the
  widget fragment URLs its own dashboard loads — same path, same
  configured parameters; only the time window (hours/range) may change.
- require_role marks its view; public_route marks the deliberately open
  ones (login, setup, health, the share page, agent ingest, install.sh,
  agent.py) with the reason. A before_request refuses any view with
  neither, so a route that forgets its decorator is closed, not open.
- /plugins/host_agent/widget and /widget/history now require viewer.
- The history widget's range buttons keep the rest of the query (and so
  a share link's token) instead of rebuilding it; the uptime widget's
  "Full SLA" link shows to logged-in users, not to share viewers.
- tests/test_route_access.py: a source scan that fails on any unmarked
  route in core or bundled plugins, the default-deny refusal, and the
  share matcher's cases.

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

steward/hosts/routes.py

@@ -288,7 +288,6 @@ async def uptime_page():
 @hosts_bp.get("/uptime/widget")
 @require_role(UserRole.viewer)
 async def uptime_widget():
-    share_token = request.args.get("s")
     async with current_app.db_sessionmaker() as db:
         result = await db.execute(select(Host).order_by(Host.name))
         hosts = result.scalars().all()
@@ -297,5 +296,4 @@ async def uptime_widget():
         "hosts/uptime_widget.html",
         hosts=hosts,
         uptime=uptime,
-        share_token=share_token,
     )