cooling.gate-off: a gate setting trips in range and is off at its far end

The acceptance catalog gains the test behind forgectrl 9e44fdc: the
coolant ceiling set just over its legal minimum must trip OVERTEMP with
a hold and fire blocked at the next run start; set to its top the engine
must skip the gate (verdict OK), report it in gates_off on /status and
/cool/status, and log the run-start line; the original values are
restored, on failure too, and proven restored. Five host cases against a
scripted engine. The cooling covers map now names the files that carry
gate state (gates, settings, status, the panel) and corrects a glob that
matched nothing: the GRBL cooling client is src/glowforge_cooling.c, not
src/gfcool*. The fake forgectrl serves /logs/tail and keeps blank form
values as "clear", which is what the daemon does with them.

Docs: COOLING.md section 8 carries each setting's legal range and
recommended band and a new 8a on turning a gate off; SAFETY.md names
what no setting can reach; ACCEPTANCE.md records that gates are
exercised through the settings API, never GFCOOL_* env overrides;
BRINGUP item 19 records the pattern as landed and the catalog is 43.

forgectrl pin moves to 9e44fdc; fetch-verified.

forgetest/tests/helpers.py

@@ -102,6 +102,7 @@ class FakeForgectrl:
             "cam": {"running": False, "clients": 0},
             "diag": {"running": False},
             "settings": {"controller_mode": "grbl", "lid_lamp_idle": ""},
+            "logs_tail": {"name": "forgectrl", "text": "", "truncated": False, "exists": True},
         }
         self.posts = []
         self.on_post = None
@@ -122,7 +123,8 @@ class FakeForgectrl:
             def do_GET(self):
                 path = self.path.split("?", 1)[0]
                 key = {"/mode": "mode", "/status": "status", "/cool/status": "cool", "/cam/status": "cam",
-                       "/diag/status": "diag", "/settings": "settings"}.get(path)
+                       "/diag/status": "diag", "/settings": "settings",
+                       "/logs/tail": "logs_tail"}.get(path)
                 if key is None:
                     return self._send(404, {"error": "no " + path})
                 self._send(200, fake.state[key])
@@ -131,7 +133,7 @@ class FakeForgectrl:
                 path, _, query = self.path.partition("?")
                 n = int(self.headers.get("Content-Length") or 0)
                 raw = self.rfile.read(n).decode() if n else ""
-                form = dict(_up.parse_qsl(raw)) if raw else dict(_up.parse_qsl(query))
+                form = dict(_up.parse_qsl(raw if raw else query, keep_blank_values=True))
                 fake.posts.append((path, form))
                 if fake.on_post:
                     r = fake.on_post(path, form)
@@ -143,6 +145,7 @@ class FakeForgectrl:
                     fake.state["settings"]["controller_mode"] = form["controller"]
                 elif path == "/settings":
                     fake.state["settings"].update(form)
+                    return self._send(200, fake.state["settings"])
                 self._send(200, {"ok": True})
 
         self._srv = http.server.ThreadingHTTPServer(("127.0.0.1", 0), H)