Tap-target check expects a pin button per WAN host row (closes #46)

The viewport harness's tap-target check required at least 10 visible
pin buttons while 26 render, so pin buttons missing from up to 16 rows
went unnoticed. It now expects one per WAN host row. The host row count
the harness gathers, which the app-rendered check also reads, counts
only the WAN host rows, since the local host rows have no pin button.
Each control's minimum is now worked out from the gathered facts.

TODO.md's harness entry no longer says every check guards itself: the
overflow, viewport-edge and clipped-text checks rely on app-rendered.

Model: opus-5-5

test/viewport/facts.js

@@ -173,7 +173,9 @@ export function collectLayoutFacts(options) {
         clipped,
         tapTargets,
         rows,
-        rowCount: document.querySelectorAll(".host-row").length,
+        // WAN host rows only: each has a pin button, and the tap-target
+        // check expects one per row. The local host rows have none.
+        wanRowCount: document.querySelectorAll("#wan-hosts .host-row").length,
         numericLatencies: Array.from(
             document.querySelectorAll(".latency-value"),
         ).filter((el) => /\d/.test(el.textContent)).length,