Fix /place 500s, /day rate-limit handling, calendar listener leak, error surfacing (#40)

- /api/v2/place still called grid.in_north_america(), which the worldwide-
  coverage change removed — every request raised AttributeError (500). The
  failure was invisible because compare.js treats the call as best-effort,
  so the instant chip-naming feature was silently dead. Drop the dead guard;
  the lat/lon Query validators already bound the inputs.
- /api/v2/day was the only data route not wrapping get_history in
  _weather_fetch_error, so a rate-limited cold cell returned a raw 500
  instead of the clean 503 the other routes emit.
- calendar: the #calendar pointerleave handler was re-registered inside
  attachHover on every render — and the comfort slider re-renders per input
  tick, stacking dozens of copies. Register it once at module scope next to
  the matching document-level dismiss handler.
- getJSON: check res.ok before parsing the body as JSON and fall back to the
  status line, so a non-JSON error body (a proxy 502 HTML page) reads as
  "Request failed (502 Bad Gateway)" instead of a JSON parse error.

static/calendar.js

@@ -208,6 +208,14 @@ document.addEventListener("pointerdown", (e) => {
   }
 });
 
+// Mouse only: hovering off the grid hides the preview. On touch the tooltip is
+// click-activated and must persist until a non-day tap (the handler above).
+// Registered once — #calendar persists across re-renders (only its cells are
+// replaced), so registering inside attachHover would stack a copy per render.
+calEl.addEventListener("pointerleave", (e) => {
+  if (e.pointerType === "mouse") document.getElementById("cal-tip").hidden = true;
+});
+
 // ---- location picker ----
 // The Find button opens the shared modal map picker; choosing a spot loads it.
 const findBtn = document.getElementById("find-btn");
@@ -841,9 +849,6 @@ function attachHover(byDate) {
       else armedCell = c;                // first tap only showed the tooltip
     });
   });
-  // Mouse only: hovering off the grid hides the preview. On touch the tooltip is
-  // click-activated and must persist until a non-day tap (see the document handler).
-  calEl.addEventListener("pointerleave", (e) => { if (e.pointerType === "mouse") tip.hidden = true; });
 }
 
 // ---- restore (hash from a shared link, else the last place you looked at) ----

static/nav.js

@@ -213,8 +213,16 @@ async function fetchStore(url, rec) {
     cachePut({ ...rec, t: Date.now(), day: localDay() });
     return rec.d;
   }
+  if (!res.ok) {
+    // Error bodies aren't always JSON (a proxy 502 serves an HTML page) — fall
+    // back to the status line rather than surfacing a JSON parse error.
+    let detail = null;
+    try { detail = (await res.json()).detail; } catch (e) {}
+    const err = new Error(detail || `Request failed (${res.status} ${res.statusText})`.trim());
+    err.status = res.status;
+    throw err;
+  }
   const d = await res.json();
-  if (!res.ok) { const err = new Error(d.detail || "request failed"); err.status = res.status; throw err; }
   cachePut({ url, t: Date.now(), day: localDay(), etag: res.headers.get("ETag") || null, d });
   return d;
 }