feat(hosts): Phase 2+3 — agent column, fold fleet + management into Hosts

- Hosts list: new Agent column (latest CPU/mem read from the generic
  PluginMetric table — no host_agent import) + an admin "Agent fleet" button.
- /plugins/host_agent/ (old fleet page) now redirects to /hosts/ (folded into
  the hub; kept as a redirect so widgets/links don't 404).
- Agent management moved off the "settings" URL: the management page is now
  /plugins/host_agent/fleet/ ("Agent fleet" — bulk provision/install/update +
  registrations + curl install), reachable from the Hosts list. Old
  /plugins/host_agent/settings/ redirects there. Per-host management lives on
  the host detail page; this page is now explicitly the bulk/fleet view.

Milestone 70 phases 2-3. Phase 4 (plugins capability/integration split + nav
cleanup) next.

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

plugins/host_agent/routes.py

@@ -375,10 +375,9 @@ async def _fleet_rows(session) -> list[dict]:
 @host_agent_bp.get("/")
 @require_role(UserRole.viewer)
 async def index():
-    """Fleet overview page — cards per host linking to the detail view."""
-    async with current_app.db_sessionmaker() as session:
-        rows = await _fleet_rows(session)
-    return await render_template("host_list.html", rows=rows)
+    """The fleet view folded into the Hosts hub — kept as a redirect so old
+    links/widgets don't 404."""
+    return redirect("/hosts/")
 
 
 @host_agent_bp.get("/widget")
@@ -571,7 +570,14 @@ async def host_panel(host_id: str):
 
 @host_agent_bp.get("/settings/")
 @require_role(UserRole.admin)
-async def settings_list():
+async def settings_redirect():
+    """Old management URL — agent management moved into the Hosts section."""
+    return redirect(url_for("host_agent.fleet"))
+
+
+@host_agent_bp.get("/fleet/")
+@require_role(UserRole.admin)
+async def fleet():
     from steward.core.capabilities import has_capability
     from steward.models.ansible_inventory import AnsibleTarget, AnsibleGroup
 
@@ -641,7 +647,7 @@ async def add_host():
         await session.commit()
         host_id = host.id
 
-    return redirect(url_for("host_agent.settings_list") + f"?new_token={raw}&host_id={host_id}")
+    return redirect(url_for("host_agent.fleet") + f"?new_token={raw}&host_id={host_id}")
 
 
 @host_agent_bp.post("/settings/<host_id>/rotate-token")
@@ -657,7 +663,7 @@ async def rotate_token(host_id: str):
         reg.token_hash = hashed
         reg.token_created_at = datetime.now(timezone.utc)
         await session.commit()
-    return redirect(url_for("host_agent.settings_list") + f"?new_token={raw}&host_id={host_id}")
+    return redirect(url_for("host_agent.fleet") + f"?new_token={raw}&host_id={host_id}")
 
 
 @host_agent_bp.post("/settings/<host_id>/delete")
@@ -670,7 +676,7 @@ async def delete_registration(host_id: str):
         if reg is not None:
             await session.delete(reg)
             await session.commit()
-    return redirect(url_for("host_agent.settings_list"))
+    return redirect(url_for("host_agent.fleet"))
 
 
 # ── Deploy via Ansible (plugin↔core synergy via the capability registry) ──────

plugins/host_agent/templates/settings_list.html

@@ -1,9 +1,16 @@
 {% extends "base.html" %}
 {% from "_macros.html" import crumbs %}
-{% block title %}Host Agent — Steward{% endblock %}
-{% block breadcrumb %}{{ crumbs([("Host Agents", "/plugins/host_agent/"), ("Settings", "")]) }}{% endblock %}
+{% block title %}Agent fleet — Steward{% endblock %}
+{% block breadcrumb %}{{ crumbs([("Hosts", "/hosts/"), ("Agent fleet", "")]) }}{% endblock %}
 {% block content %}
-<h1 class="page-title">Host Agent — Registered Hosts</h1>
+<div style="display:flex;align-items:center;justify-content:space-between;margin-bottom:1rem;gap:1rem;flex-wrap:wrap;">
+  <h1 class="page-title" style="margin-bottom:0;">Agent fleet</h1>
+  <a href="/hosts/" class="btn btn-ghost btn-sm">← Hosts</a>
+</div>
+<p style="color:var(--text-muted);font-size:0.84rem;margin:-0.4rem 0 1.25rem;">
+  Bulk agent operations across your inventory. For a single host, use its
+  <a href="/hosts/">host page</a> — provisioning and metrics live there.
+</p>
 
 {% if new_token %}
 <div class="card" style="background:var(--accent-bg);">
@@ -58,7 +65,7 @@
       No managed SSH key yet — Steward needs one to log into hosts as <code>steward</code>.
     </span>
     <form method="post" action="/settings/ansible/generate-key" style="margin:0;">
-      <input type="hidden" name="next" value="/plugins/host_agent/settings/">
+      <input type="hidden" name="next" value="/plugins/host_agent/fleet/">
       <button type="submit" class="btn btn-sm">Generate managed key</button>
     </form>
   </div>