fix: the locale runtime the card ships is the code the tests prove (#354)

The production LANGUAGE_RUNTIME was a handwritten twin of the tested
LanguageRuntime class (germanDictionary/Pending/Failed): equivalent on the
day it was written, invisible to every i18n-runtime test afterwards. The
registry now exports one page-scoped `new LanguageRuntime(LANGUAGE_REGISTRY,
…)` instance — the whole existing suite starts proving the object production
actually runs, and a contract unit (instanceof + source free of the old
field names) keeps the duplicate from returning.

The class gains an optional `loadFailed(code)` hook — fired once when a
dictionary load settles into English fallback — and the registry fans it out
through `subscribeLanguageLoadFailures`. Only the View card subscribes (it
alone owns toast infrastructure): a failed language pack now shows the new
`toast.locale_load_failed` message (en/ru/de) instead of a console-only
warning; space card and both GUI editors keep the console warning as before.

Proofs: contract unit, hook unit, subscription unit; smoke_german_locale
extended — the both-attempts-failed scenario now asserts the visible toast;
two new registry mutants (handwritten-twin returns, toast dropped).

Issue: #354
User-Visible: yes

docs/images/screenshots.json

@@ -3,7 +3,7 @@
   "fixture": "synthetic-only",
   "chromium": "151.0.7922.34",
   "oxipng": null,
-  "sourceFingerprint": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+  "sourceFingerprint": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
   "captureScriptSha256": "fe76c8e2e27501e9a377d7aa15dd6cba6a018d55c07deb602dbee097f0a0a5ba",
   "command": "npm run build && node demo/docs/capture.mjs",
   "scenarios": {
@@ -15,8 +15,8 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
-      "imageSha256": "78d328498bd17a9ee1ec44b389d244b61fca9ac52c9aad6631aa85c53233fec0"
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
+      "imageSha256": "0ca982495a7749907c48ebbddfd089c54385a4347f79f64e94af2c5a8d5c03eb"
     },
     "view-touch": {
       "file": "02-view-touch.png",
@@ -26,7 +26,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "3be239a5a494f6776540a9c0049694ee6f9d2ba927c8bcb4b26ee5a69a228a7d"
     },
     "space-create": {
@@ -37,7 +37,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "a55b463055a565892ca139014e314a8f63fb5301c87fff2e48d7e69210fe9b6c"
     },
     "room-contour-close": {
@@ -48,7 +48,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "dfad9a27371cfa397a3fd8dce7005f42d24649743f5322105ee894067d3a9f16"
     },
     "plan-context-tray": {
@@ -59,7 +59,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "b75f348c632296da5c2fc142d53df613f757e1516acac315be50f5b4557729cc"
     },
     "device-editor": {
@@ -70,7 +70,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "8affadfce926fe2f6cf344c33f611c44fcbc79c1969f69c3a6935ff2e99c36c3"
     },
     "device-display-preview": {
@@ -81,8 +81,8 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
-      "imageSha256": "6f628abe6b89d7c4b352e6d73ac0b126526f6fdba5927bb774c5b884e484ca19"
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
+      "imageSha256": "6d323b6f641b2cc7db64252f70567348bd3f2551f82e61fd3a2b4674d244918e"
     },
     "background-editor": {
       "file": "07-background-editor.png",
@@ -92,7 +92,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "a1d1a905f1410f73231d2ea5d1dfbd8ae79c2fe8b0a79cff87ebb977ac7a3103"
     },
     "room-card": {
@@ -103,7 +103,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "48a5685039a5e0de2a28190d857b193c86e2e63606e3c7a8c40fc9d2b190da4e"
     },
     "device-info": {
@@ -114,7 +114,7 @@
       },
       "theme": "dark",
       "language": "en",
-      "sourceSha256": "20360427643d04e7068255e2a64cbdb296bfc772d8c11cfeb0baf753520addb5",
+      "sourceSha256": "f8b80b1f920fa0ecaa24abd1ae6c143df1921d892546a22a44831b2b688f7fd0",
       "imageSha256": "29a342811aaedaebc54ba337792d60cb454a7cf4c3063b210f6c4bafe0a4d87b"
     }
   }