feat(settings): Phase 4 — capabilities vs integrations + nav cleanup

Final phase of the host-IA unification (milestone 70).

- Settings → Plugins split into two tiers: "Monitoring capabilities"
  (host_agent, http, snmp, docker — built-in host facets, surfaced via
  Hosts/Status, on by default) and "Integrations" (traefik, unifi — external
  systems, off until configured). Presentation only: a CAPABILITY_PLUGINS set
  (overridable by plugin.yaml `kind:`) tags each plugin; module loading,
  optional deps, and migrations are untouched.
- Drop the "default-enable a plugin" framing in the UI copy — capabilities are
  described as built-in, not optional add-ons.
- Nav: remove the standalone "Uptime" item (folded into Hosts; still reachable
  via the SLA button on the Hosts list).

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

steward/settings/routes.py

@@ -505,6 +505,13 @@ def _build_plugin_cfg_from_form(plugin: dict, form) -> dict:
 
 # ── Plugins list ──────────────────────────────────────────────────────────────
 
+# Bundled plugins that are really built-in *host/monitoring capabilities* (facets
+# of a host), not discrete vendor integrations. Presentation-only split — they
+# still load through the normal plugin mechanism. A plugin.yaml may set
+# kind: capability|integration to override.
+CAPABILITY_PLUGINS = {"host_agent", "http", "snmp", "docker"}
+
+
 @settings_bp.get("/plugins/")
 @require_role(UserRole.admin)
 async def plugins():
@@ -512,9 +519,14 @@ async def plugins():
         settings = await get_all_settings(db)
     discovered = _discover_plugins()
     _merge_plugin_config(discovered, to_plugins_cfg(settings))
+    for p in discovered:
+        p["_kind"] = p.get("kind") or (
+            "capability" if p["_dir"] in CAPABILITY_PLUGINS else "integration")
     repos = _get_plugin_repos(settings)
     return await render_template(
         "settings/plugins.html",
+        capabilities=[p for p in discovered if p["_kind"] == "capability"],
+        integrations=[p for p in discovered if p["_kind"] != "capability"],
         discovered_plugins=discovered,
         repos=repos,
         settings=settings,