Make the map editor accept a click, and unclutter its panel

Clicking the map in the editor did nothing, ever. The click handler was bound
inside `if (props.pickerMode)` at mount, and the editor mounts with no asset
selected, so the handler was never attached; selecting an asset flipped the prop
but nothing rebound it. The asset forms were unaffected because their picker
mounts inside a modal that is already in picker mode, which is why this looked
like an editor-only fault. The handler is now bound unconditionally and
handleMapClick keeps its own picker-mode guard.

Verified in a browser against the dev instance, both ways: with the old binding
a click on a selected asset produced no position at all; with the fix the same
click reports 1652, 1138.

Markers are now drawn in picker mode too. Placing one relative to the machines
already on the floor is the entire task, and the old code skipped rendering them
whenever the map was a picker.

Two things that looked like stray widgets:
- The editor's panel header put a heading and three controls on one row inside a
  320px panel, squeezing the search box until its placeholder read "Search na".
  The heading takes its own row and the controls share the next.
- The legend drew its bar and border even with nothing to put in it, which read
  as an empty input box under the toolbar. It renders only when it has entries.

frontend/src/views/MapEditor.vue

@@ -518,13 +518,27 @@ function cancelEdit() {
 }
 
 .panel-header {
+  /* The heading takes its own row and the three controls share the next one(s).
+     All four on a single row inside a 320px panel squeezed the search box until
+     its placeholder read "Search na". */
   display: flex;
-  justify-content: space-between;
+  flex-wrap: wrap;
+  gap: 0.5rem;
   align-items: center;
   padding: 1rem;
   border-bottom: 1px solid var(--border);
 }
 
+.panel-header h3 {
+  flex: 1 1 100%;
+}
+
+.panel-header .form-control {
+  /* Shrinkable and equal, so nothing gets crushed to fit a sibling. */
+  flex: 1 1 8rem;
+  min-width: 0;
+}
+
 .panel-header h3 {
   margin: 0;
   font-size: 1rem;