revert: Opus 4.7 default effort back to Extra High (xhigh)

Reverts the user-facing default chosen in 4c32418 ("set Opus 4.7
default effort to High"). Per request, Extra High is the preferred
default. Adapter test updated: with xhigh default, the SDK receives
`max` (per the existing xhigh→max mapping in ClaudeAdapter).

Author: tyulyukov

apps/server/src/provider/Layers/ClaudeAdapter.test.ts

@@ -353,7 +353,7 @@ describe("ClaudeAdapterLive", () => {
     );
   });
 
-  it.effect("defaults Claude Opus 4.7 sessions to high effort", () => {
+  it.effect("defaults Claude Opus 4.7 sessions to xhigh effort", () => {
     const harness = makeHarness();
     return Effect.gen(function* () {
       const adapter = yield* ClaudeAdapter;
@@ -368,7 +368,7 @@ describe("ClaudeAdapterLive", () => {
       });
 
       const createInput = harness.getLastCreateQueryInput();
-      assert.equal(createInput?.options.effort, "high");
+      assert.equal(createInput?.options.effort, "max");
     }).pipe(
       Effect.provideService(Random.Random, makeDeterministicRandomService()),
       Effect.provide(harness.layer),

apps/server/src/provider/Layers/ClaudeProvider.ts

@@ -54,8 +54,8 @@ const BUILT_IN_MODELS: ReadonlyArray<ServerProviderModel> = [
       reasoningEffortLevels: [
         { value: "low", label: "Low" },
         { value: "medium", label: "Medium" },
-        { value: "high", label: "High", isDefault: true },
-        { value: "xhigh", label: "Extra High" },
+        { value: "high", label: "High" },
+        { value: "xhigh", label: "Extra High", isDefault: true },
         { value: "max", label: "Max" },
         { value: "ultrathink", label: "Ultrathink" },
       ],