fix(layers): translate every route proxy refusal and clear stale receiver errorText

The route proxy also refuses with 'routing busy — too many routes at once'
(429) and 'route proxy error'; both showed in English in every locale.
Mark them in ROUTING_REFUSALS and add es, ru, zh-CN and zh-Hant entries.

errorText is now cleared on a new connection, a mode switch and stop(), so
it never outlives the error it describes. Tests cover the two refusals,
'Routing failed: rate limited' (pattern order) and the stop() reset.

changelog.d/1209-layer-errors-english-in-data.md

@@ -1,4 +1,5 @@
 - Keep Directions route errors, the Local ADS-B receiver error and Global
   Context cohort reasons English in layer data; the Layers panel, Radio card
-  and awareness panel still show them in the interface language
-  (daikaginza, #1209).
+  and awareness panel still show them in the interface language. The route
+  proxy's "routing busy" and "route proxy error" refusals are now translated
+  too (daikaginza, #1209).