refactor(hosts): remove legacy host_agent redirects/paths (no back-compat)

Dev-only instance, no bookmarks — per family rule 22, fully remove old paths
instead of shimming them.

- Delete the /plugins/host_agent/ (index) and /plugins/host_agent/settings/
  redirect routes; delete the now-dead host_list.html fleet template.
- Move the remaining management POST routes off /settings/ to /fleet/
  (add-host, rotate-token, delete) — single canonical prefix.
- Repoint real callers to canonical URLs: dashboard widgets (host resources →
  /hosts/, history → /plugins/host_agent/fleet/), the full-metrics page
  breadcrumb + back link (→ the host hub), Settings→Ansible link, and the
  agent panel's curl-install link.

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

plugins/host_agent/routes.py

@@ -372,14 +372,6 @@ async def _fleet_rows(session) -> list[dict]:
     return rows
 
 
-@host_agent_bp.get("/")
-@require_role(UserRole.viewer)
-async def index():
-    """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")
 async def widget_table():
     """Fleet-glance dashboard widget: one row per monitored host, latest metrics."""
@@ -568,13 +560,6 @@ async def host_panel(host_id: str):
     )
 
 
-@host_agent_bp.get("/settings/")
-@require_role(UserRole.admin)
-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():
@@ -618,7 +603,7 @@ async def fleet():
     )
 
 
-@host_agent_bp.post("/settings/add-host")
+@host_agent_bp.post("/fleet/add-host")
 @require_role(UserRole.admin)
 async def add_host():
     form = await request.form
@@ -650,7 +635,7 @@ async def add_host():
     return redirect(url_for("host_agent.fleet") + f"?new_token={raw}&host_id={host_id}")
 
 
-@host_agent_bp.post("/settings/<host_id>/rotate-token")
+@host_agent_bp.post("/fleet/<host_id>/rotate-token")
 @require_role(UserRole.admin)
 async def rotate_token(host_id: str):
     async with current_app.db_sessionmaker() as session:
@@ -666,7 +651,7 @@ async def rotate_token(host_id: str):
     return redirect(url_for("host_agent.fleet") + f"?new_token={raw}&host_id={host_id}")
 
 
-@host_agent_bp.post("/settings/<host_id>/delete")
+@host_agent_bp.post("/fleet/<host_id>/delete")
 @require_role(UserRole.admin)
 async def delete_registration(host_id: str):
     async with current_app.db_sessionmaker() as session: