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>

plugins/host_agent/routes.py

@@ -9,7 +9,7 @@ from pathlib import Path
 
 import secrets
 from quart import Blueprint, current_app, jsonify, request, Response, render_template, redirect, url_for, session
-from steward.auth.middleware import require_role
+from steward.auth.middleware import public_route, require_role
 from steward.models.users import UserRole
 from sqlalchemy import select, func, or_, and_
 from datetime import timedelta
@@ -166,6 +166,7 @@ def _error(status: int, code: str, detail: str | None = None) -> tuple[Any, int]
 
 
 @host_agent_bp.post("/ingest")
+@public_route("the agent authenticates with its bearer token")
 async def ingest():
     auth = request.headers.get("Authorization", "")
     if not auth.startswith("Bearer "):
@@ -313,6 +314,7 @@ def _agent_version() -> str:
 
 
 @host_agent_bp.get("/install.sh")
+@public_route("fetched by curl on the host being enrolled; carries an enrolment token")
 async def install_script():
     token = request.args.get("token", "")
     if not token:
@@ -344,6 +346,7 @@ async def install_script():
 
 
 @host_agent_bp.get("/agent.py")
+@public_route("fetched by the installer and by agent self-update; holds no secrets")
 async def agent_source():
     try:
         body = AGENT_SOURCE_PATH.read_text(encoding="utf-8")
@@ -470,6 +473,7 @@ async def _fleet_rows(session) -> list[dict]:
 
 
 @host_agent_bp.get("/widget")
+@require_role(UserRole.viewer)
 async def widget_table():
     """Fleet-glance dashboard widget: one row per monitored host, latest metrics."""
     async with current_app.db_sessionmaker() as session:
@@ -478,6 +482,7 @@ async def widget_table():
 
 
 @host_agent_bp.get("/widget/history")
+@require_role(UserRole.viewer)
 async def widget_history():
     host_id = request.args.get("host_id", "")
     try: