feat: replace Claude with GPT for AI chat integration

- Replace ClaudeAdapter with GPTAdapter using OpenAI GPT (gpt-5-mini)
- Implement function calling for calendar operations (getDay, proposeCreate/Update/Delete, searchEvents)
- Add provider-agnostic AI utilities in ai/utils/ (systemPrompt, toolDefinitions, toolExecutor, eventFormatter)
- Add USE_TEST_RESPONSES env var to toggle between real AI and test responses
- Switch ChatService.processMessage to use real AI provider
- Add npm run format command for Prettier
- Update CLAUDE.md with new architecture

package-lock.json

@@ -62,13 +62,13 @@
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         "dotenv": "^16.4.7",
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         "jsonwebtoken": "^9.0.3",
         "mongoose": "^9.1.1",
+        "openai": "^6.15.0",
         "rrule": "^2.8.1"
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@@ -106,26 +106,6 @@
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-    "node_modules/@anthropic-ai/sdk": {
-      "version": "0.71.2",
-      "resolved": "https://registry.npmjs.org/@anthropic-ai/sdk/-/sdk-0.71.2.tgz",
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-      "license": "MIT",
-      "dependencies": {
-        "json-schema-to-ts": "^3.1.1"
-      },
-      "bin": {
-        "anthropic-ai-sdk": "bin/cli"
-      },
-      "peerDependencies": {
-        "zod": "^3.25.0 || ^4.0.0"
-      },
-      "peerDependenciesMeta": {
-        "zod": {
-          "optional": true
-        }
-      }
-    },
     "node_modules/@babel/code-frame": {
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@@ -11252,6 +11232,27 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/openai": {
+      "version": "6.15.0",
+      "resolved": "https://registry.npmjs.org/openai/-/openai-6.15.0.tgz",
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+      "license": "Apache-2.0",
+      "bin": {
+        "openai": "bin/cli"
+      },
+      "peerDependencies": {
+        "ws": "^8.18.0",
+        "zod": "^3.25 || ^4.0"
+      },
+      "peerDependenciesMeta": {
+        "ws": {
+          "optional": true
+        },
+        "zod": {
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     "node_modules/optionator": {
       "version": "0.9.4",
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