feat(landing): add a live system status indicator to the footer (#641)

Adds /api/status to the landing Pages worker, HEAD-probing demo.snapotter.com and
docs.snapotter.com with a 2 second per-attempt deadline and one retry. snapotter.com is
not probed; the worker answering the request is the proof it is up.

The footer badge ships grey in the static HTML and only upgrades once the route answers.
A rejected fetch, a non-ok response, an unparseable body, and an unrecognized verdict all
leave it grey, so it never claims green on its own.

Color lives in the dot, never the label: `--color-success` scores 4.498:1 against the
footer's `--color-background-alt`, just under AA.

Four labels across 21 locales.

tests/unit/palette-contrast.test.ts

@@ -159,4 +159,13 @@ describe("landing", () => {
     expectPair(landing, "muted", "background");
     expectPair(landing, "dark-fg", "dark-bg");
   });
+
+  // The footer status dot is a graphic, so WCAG 1.4.11's 3:1 applies rather
+  // than AA's 4.5. Note "success" clears 3:1 here but not 4.5, which is why the
+  // badge's label stays muted while only the dot takes a state color.
+  it("footer status dot clears 3:1 non-text on the footer surface", () => {
+    for (const dot of ["muted", "success", "primary-ink", "danger"]) {
+      expectPair(landing, dot, "background-alt", 3);
+    }
+  });
 });