feat(json-editor): add reusable JSON code editor

- introduce a shared themed JSON editor with line numbers, formatting, status feedback, and keyboard editing helpers.
- use the shared editor in model pricing JSON mode so pricing maps get consistent editor behavior.
- localize structured JSON validation messages so parse errors avoid browser-specific English text.

web/default/src/i18n/locales/en.json

@@ -679,6 +679,7 @@
     "Check for updates": "Check for updates",
     "Check in daily to receive random quota rewards": "Check in daily to receive random quota rewards",
     "Check in now": "Check in now",
+    "Check line {{line}} for a missing comma.": "Check line {{line}} for a missing comma.",
     "Check out the Quick Start": "Check out the Quick Start",
     "Check resolved IPs against IP filters even when accessing by domain": "Check resolved IPs against IP filters even when accessing by domain",
     "Check-in failed": "Check-in failed",
@@ -1527,6 +1528,7 @@
     "Expand": "Expand",
     "Expand All": "Expand All",
     "Expected a JSON array.": "Expected a JSON array.",
+    "Expected a JSON array of group identifiers": "Expected a JSON array of group identifiers",
     "Experiment with prompts and models in real time.": "Experiment with prompts and models in real time.",
     "Expiration Time": "Expiration Time",
     "expired": "expired",
@@ -2093,6 +2095,9 @@
     "JSON Editor": "JSON Editor",
     "JSON format error": "JSON format error",
     "JSON format supports service account JSON files": "JSON format supports service account JSON files",
+    "JSON is invalid at line {{line}}, column {{column}}.": "JSON is invalid at line {{line}}, column {{column}}.",
+    "JSON is invalid at position {{position}}.": "JSON is invalid at position {{position}}.",
+    "JSON is invalid. Please check the syntax.": "JSON is invalid. Please check the syntax.",
     "JSON map of group → description exposed when users create API keys.": "JSON map of group → description exposed when users create API keys.",
     "JSON map of group → ratio applied when the user selects the group explicitly.": "JSON map of group → ratio applied when the user selects the group explicitly.",
     "JSON map of model → multiplier applied to quota billing.": "JSON map of model → multiplier applied to quota billing.",
@@ -2101,6 +2106,7 @@
     "JSON Mode": "JSON Mode",
     "JSON must be an object": "JSON must be an object",
     "JSON object:": "JSON object:",
+    "JSON structure is invalid": "JSON structure is invalid",
     "JSON Text": "JSON Text",
     "JSON-based access control rules. Leave empty to allow all users.": "JSON-based access control rules. Leave empty to allow all users.",
     "Just now": "Just now",
@@ -4313,6 +4319,7 @@
     "Validity Period": "Validity Period",
     "Value": "Value",
     "Value (supports JSON or plain text)": "Value (supports JSON or plain text)",
+    "Value is required": "Value is required",
     "Value must be at least 0": "Value must be at least 0",
     "Value Regex": "Value Regex",
     "variable": "variable",