Homepage (TDD slice 1): the status checker core

Full TDD (Q36): red test first, then the minimal implementation.
- tests/homepage_checker.bats: seam = homepage-status.py <services.json>
  <out.json>. Asserts an open port is up, a closed port is down, a wip
  service is wip (not probed), and the output carries generated_at.
- scripts/homepage-status.py: reads the config, probes each backend (tcp,
  5 s timeout), skips wip, writes status.json atomically (temp + rename).

Remaining slices: http probe method, services.json schema, the pages +
theme + toggle, the Caddyfile (validate + two hashes), the git-driven deploy.

tests/homepage_checker.bats

@@ -0,0 +1,45 @@
+#!/usr/bin/env bats
+# Seam: scripts/homepage-status.py <services.json> <out.json>
+# Given a service config, the checker writes a valid status.json with the
+# correct state per service: an open port is up, a closed port is down,
+# a wip service is wip (not probed). The output carries generated_at.
+
+load helpers
+
+setup() {
+    CHECKER="$REPO_ROOT/scripts/homepage-status.py"
+    TMP="$(mktemp -d)"
+    UP_PORT=18899
+    DOWN_PORT=18900
+    # Hold a TCP listener on UP_PORT so a probe of it succeeds.
+    python3 -c 'import socket,time; s=socket.socket(); s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1); s.bind(("127.0.0.1",'"$UP_PORT"')); s.listen(5); time.sleep(300)' &
+    LISTENER_PID=$!
+    sleep 0.5
+}
+
+teardown() {
+    [ -n "${LISTENER_PID:-}" ] && kill "$LISTENER_PID" 2>/dev/null
+    rm -rf "$TMP"
+}
+
+@test "checker: open port is up, closed port is down, wip is wip" {
+    local svc="$TMP/services.json" out="$TMP/status.json"
+    cat > "$svc" <<JSON
+[
+  {"name":"up","category":"user","probe":"127.0.0.1:$UP_PORT","method":"tcp","wip":false},
+  {"name":"down","category":"user","probe":"127.0.0.1:$DOWN_PORT","method":"tcp","wip":false},
+  {"name":"wip","category":"user","probe":"127.0.0.1:1","method":"tcp","wip":true}
+]
+JSON
+    python3 "$CHECKER" "$svc" "$out"
+    [ -f "$out" ]
+    python3 - "$out" <<'PY'
+import json, sys
+d = json.load(open(sys.argv[1]))
+s = {x["name"]: x["state"] for x in d["services"]}
+assert s["up"] == "up", s
+assert s["down"] == "down", s
+assert s["wip"] == "wip", s
+assert "generated_at" in d
+PY
+}