chore(ui,agent): harden collector parsing, drop dead CSS, resilver label

Addresses final code review:
- to_int/1 now returns 0 on nil or unparseable strings instead of crashing
- remove unused .pool-row CSS (superseded by .pool-block)
- clamp capacity bar width to [0, 100] to prevent visual overflow
- pool_scrub_line/1 uses scan_function so resilver shows as "resilver..."

server/test/server_web/live/host_detail_live_test.exs

@@ -46,7 +46,7 @@ defmodule ServerWeb.HostDetailLiveTest do
             "error_count" => 2,
             "vdev_count" => 1,
             "degraded_vdev_count" => 1,
-            "scan_function" => "scrub",
+            "scan_function" => "resilver",
             "scan_state" => "SCANNING",
             "last_scrub_end" => nil,
             "vdevs" => [
@@ -117,7 +117,7 @@ defmodule ServerWeb.HostDetailLiveTest do
     assert html =~ "tank"
     assert html =~ "DEGRADED"
     assert html =~ "raidz2"
-    assert html =~ "scrub scanning"
+    assert html =~ "resilver scanning"
     assert html =~ "raidz2-0 DEGRADED"
     assert html =~ "cksum=2"
     assert html =~ "callout err"