A field can be a place, and a question can be about one

`type: location` puts a pin on a map and stores {lat, lon, zoom}; a
record that holds one renders as a still, on a desk and in any
resource card. `place:` on a question is the counterpart to `event:`:
event makes a page an occasion with a time, place makes it somewhere,
shows the map under the question, and opens any location field on the
page there instead of on the globe.

Every tile and every still is fetched by portal and served from this
origin (src/maps.rs, MapLibre vendored in public/), so a page with a
map on it still talks to nobody but us: no third-party request, no
consent banner, and the token never leaves the server. MAPBOX_TOKEN
unset turns the whole thing off, the way GARAGE_* does for uploads.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/content/validate.rs

@@ -124,6 +124,11 @@ pub fn validate_questions(
                 anyhow::bail!("question {:?}: event: {e}", question.id);
             }
         }
+        if let Some(place) = &question.place {
+            if let Err(e) = place.validate() {
+                anyhow::bail!("question {:?}: place: {e}", question.id);
+            }
+        }
         if let Some(target) = &question.requires_chain {
             if !questions.contains_key(target) {
                 anyhow::bail!(
@@ -246,6 +251,30 @@ pub fn validate_questions(
                             question.id, alternative.name, feature.name, requirement.name
                         );
                     }
+                    if requirement.kind == "location" {
+                        if requirement.resource.is_some() || requirement.bind.is_some() {
+                            anyhow::bail!(
+                                "question {:?} alternative {:?} feature {:?}: requirement {:?} is type: location - the visitor puts the pin, it can't also load one from a resource or bind",
+                                question.id, alternative.name, feature.name, requirement.name
+                            );
+                        }
+                        // `value` opens the map somewhere useful. It is
+                        // the content author's own coordinates, so a
+                        // typo here is a map of the Atlantic.
+                        if let Some(value) = &requirement.value {
+                            let parts: Vec<&str> = value.split(',').map(str::trim).collect();
+                            let ok = (2..=3).contains(&parts.len())
+                                && parts.iter().all(|p| p.parse::<f64>().is_ok())
+                                && parts[0].parse::<f64>().is_ok_and(|lat| (-90.0..=90.0).contains(&lat))
+                                && parts[1].parse::<f64>().is_ok_and(|lon| (-180.0..=180.0).contains(&lon));
+                            if !ok {
+                                anyhow::bail!(
+                                    "question {:?} alternative {:?} feature {:?}: requirement {:?} is type: location - its `value` opens the map and must be `lat,lon` or `lat,lon,zoom`, not {value:?}",
+                                    question.id, alternative.name, feature.name, requirement.name
+                                );
+                            }
+                        }
+                    }
                     if let Some(bind) = &requirement.bind {
                         if bind.field == requirement.name
                             || !sibling_names.contains(bind.field.as_str())