command block and colour picker keyed

ColorPicker's one string was placeholder="Font Weight" on an <input type="color">,
where a placeholder is both wrong text and inert — browsers do not render one on a
colour input. Keyed it as ui.colorPicker.placeholder and moved it to the hex text
field beside it, which is a real text input and had none. Translating it in place
would have created a key guaranteed never to be seen.

Both files still have no importers; CommandBlock stays because commands the user
might run need a copy button by convention.

src/workspaces/components/locales/en-GB.json

@@ -17,6 +17,13 @@
   "tabs": {
     "filterPlaceholder": "Filter"
   },
+  "commandBlock": {
+    "run": "Run in terminal",
+    "copy": "Copy command"
+  },
+  "colorPicker": {
+    "placeholder": "Hex colour"
+  },
   "state": {
     "loading": "Loading…"
   },