feat(status): unified Status page + widget across ping/DNS/HTTP monitors

Adds a Kuma-style "is everything up?" surface that aggregates heterogeneous
monitor types via a status-source registry (steward/core/status.py): each
type registers an async source(db) -> [StatusEntry]. Core registers ping/DNS;
the http plugin registers its own from setup() so core never imports plugin
tables. Per entry: current up/down, last-30 heartbeat bar, uptime %
(24h/7d/30d), latest latency + response sparkline, and TLS expiry countdown
(HTTP). New /status page (live htmx refresh) + a status_overview dashboard
widget + nav link. Pure-function unit tests for registry + sparkline.

First deliverable of milestone #68 (task #866).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/app.py

@@ -98,6 +98,7 @@ def create_app(
     from .hosts.routes import hosts_bp
     from .ping.routes import ping_bp
     from .dns.routes import dns_bp
+    from .status.routes import status_bp
     from .alerts.routes import alerts_bp
     from .ansible.routes import ansible_bp
     from .ansible.inventory_routes import inventory_bp
@@ -109,12 +110,19 @@ def create_app(
     app.register_blueprint(hosts_bp)
     app.register_blueprint(ping_bp)
     app.register_blueprint(dns_bp)
+    app.register_blueprint(status_bp)
     app.register_blueprint(alerts_bp)
     app.register_blueprint(ansible_bp)
     app.register_blueprint(inventory_bp)
     app.register_blueprint(settings_bp)
     app.register_blueprint(audit_bp)
 
+    # Register the core (ping/DNS) status sources for the unified Status page.
+    # Plugins register their own sources from setup() (e.g. http). Idempotent.
+    from .core.status import register_status_source, ping_status_source, dns_status_source
+    register_status_source(ping_status_source)
+    register_status_source(dns_status_source)
+
     # ── 8. Build task registry ─────────────────────────────────────────────────
     app._task_registry = []