feat(error-handling): Implement comprehensive gateway error handling with user-friendly messages

- Add comprehensive gateway error handler with friendly user messages
- Handle subscription status errors (inactive BYOK, subscription required)
- Handle authentication errors (invalid API keys, missing tokens)
- Handle rate limiting with retry suggestions
- Handle model availability and validation errors
- Handle network connectivity issues
- Provide actionable solutions for each error type
- Prevent duplicate error messages by returning early after showing friendly error
- Fix telemetry tests to use correct environment variable names (TASKMASTER_API_KEY)
- Fix config manager getUserId function to properly save default userId to file
- All tests now passing (34 test suites, 360 tests)

tests/unit/config-manager.test.js

@@ -89,10 +89,10 @@ const DEFAULT_CONFIG = {
     },
   },
   account: {
-    userId: null,
-    userEmail: "",
+    userId: "1234567890",
+    email: "",
     mode: "byok",
-    telemetryEnabled: false,
+    telemetryEnabled: true,
   },
 };
 
@@ -333,7 +333,6 @@ describe("getConfig Tests", () => {
       },
       global: { ...DEFAULT_CONFIG.global, ...VALID_CUSTOM_CONFIG.global },
       account: { ...DEFAULT_CONFIG.account },
-      ai: {},
     };
     expect(config).toEqual(expectedMergedConfig);
     expect(fsExistsSyncSpy).toHaveBeenCalledWith(MOCK_CONFIG_PATH);
@@ -357,7 +356,6 @@ describe("getConfig Tests", () => {
       },
       global: { ...DEFAULT_CONFIG.global, ...PARTIAL_CONFIG.global },
       account: { ...DEFAULT_CONFIG.account },
-      ai: {},
     };
     expect(config).toEqual(expectedMergedConfig);
     expect(fsReadFileSyncSpy).toHaveBeenCalledWith(MOCK_CONFIG_PATH, "utf-8");
@@ -463,7 +461,6 @@ describe("getConfig Tests", () => {
       },
       global: { ...DEFAULT_CONFIG.global, ...INVALID_PROVIDER_CONFIG.global },
       account: { ...DEFAULT_CONFIG.account },
-      ai: {},
     };
     expect(config).toEqual(expectedMergedConfig);
   });