refactor(hosts): group host modules into per-feature directories

file-manager/, metrics/ (incl. widgets, managers, alert-engine),
terminal/, tmux/ and tunnel/ each own their files; docker/ gains
container-runtime. Genuinely shared helpers (jump-host chain, host
resolver, connection pool, opkssh, vault, serial) stay at hosts/ root.
Pure file moves with import path updates; mirrored test paths follow.

src/backend/tests/hosts/metrics/widgets/temperature-collector.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import {
+  parseSensorsOutput,
+  parseSysfsThermalOutput,
+} from "../../../../hosts/metrics/widgets/temperature-collector.js";
+
+describe("temperature collectors", () => {
+  it("parses sysfs thermal zone output", () => {
+    const result = parseSysfsThermalOutput(
+      "x86_pkg_temp\t51000\nacpitz\t42\nbad\tnope\n",
+    );
+
+    expect(result).toEqual([
+      { label: "x86_pkg_temp", celsius: 51 },
+      { label: "acpitz", celsius: 42 },
+    ]);
+  });
+
+  it("parses lm-sensors temperature lines", () => {
+    const result = parseSensorsOutput(`
+coretemp-isa-0000
+Adapter: ISA adapter
+Package id 0:  +52.0°C  (high = +80.0°C, crit = +100.0°C)
+Core 0:        +48.5°C
+fan1:          1200 RPM
+`);
+
+    expect(result).toEqual([
+      { label: "Package id 0", celsius: 52 },
+      { label: "Core 0", celsius: 48.5 },
+    ]);
+  });
+});