Add z.ai/GLM provider via per-process Claude CLI env injection

Route glm:-prefixed models through the CLI/Anthropic path: ResolveModelId
strips the glm: prefix, and CreateCliStartInfo activates the z.ai
Anthropic-compatible endpoint (ANTHROPIC_BASE_URL/AUTH_TOKEN) only for that
process when IsZaiModel matches, leaving every other request's OAuth login
untouched. GLM model list is loaded through the existing model cache and
exposed via /api/models/glm with a "GLM (z.ai)" optgroup in the agent form.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Services/ServerSettingsService.cs

@@ -38,6 +38,7 @@ public class ServerSettingsService
         new SettingDefinition( "HuggingFaceToken",   "string", "",      "HuggingFace Token (optional, erhöht Rate-Limits)",            "password" ),
         new SettingDefinition( "NvidiaApiKey",       "string", "",      "Nvidia API-Key (direkt statt g4f.space Proxy)",                "password" ),
         new SettingDefinition( "MinimaxApiKey",      "string", "",      "MiniMax API-Key (für minimax-Provider im Chat)",               "password" ),
+        new SettingDefinition( "ZaiApiKey",          "string", "",      "z.ai API-Key (für GLM-Modelle über die Claude CLI)",           "password" ),
         new SettingDefinition( "ScannerKeyTypes",    "string_array", "anthropic_oauth,krea_ai", "Key-Scanner: Aktive Key-Typen",                               "checkboxes" ),
     };