test(client): bind Model Studio fixture key to its selected route

The Messages body fixture selected the Anthropic variant but placed its literal test key in the primary provider table. Exact runtime identity now exposes that invalid fixture setup. Place the literal beside the fixture endpoint; durable secret-store family sharing remains separately covered and production credential resolution is unchanged.

Validation:25 related Model Studio/catalog/shared-secret-store regressions passed,0 failed,11681 unrelated tests skipped, no retries. Formatting and diff checks passed. Prior combined workspace run:14280 passed,1 failed,14 skipped; sole failure was this fixture. Complete runtime gate is rerun after this correction. Root npm scripts unavailable (0 tests); web tree remains at407/0 proven source.

crates/tui/src/client/anthropic.rs

@@ -997,14 +997,10 @@ mod tests {
         let config = crate::config::Config {
             provider: Some("modelstudio-token-plan-anthropic".to_string()),
             providers: Some(crate::config::ProvidersConfig {
-                // All four plan/dialect variants share one key slot
-                // (modelstudio-token-plan); only the base URL is read from the
-                // anthropic entry.
-                modelstudio_token_plan: crate::config::ProviderConfig {
-                    api_key: Some("test-key".to_string()),
-                    ..Default::default()
-                },
+                // Durable secret-store keys share a family slot, but a literal
+                // config key belongs to the selected route's own table.
                 modelstudio_token_plan_anthropic: crate::config::ProviderConfig {
+                    api_key: Some("test-key".to_string()),
                     base_url: Some(base_url.to_string()),
                     ..Default::default()
                 },