feat(tests): add comprehensive happy path tests for session lifecycle

- Implemented session cleanup tests to ensure proper handling of session completions and cleanup operations.
- Added session initialization tests to verify session creation and observation queuing on first tool use.
- Created session summary tests to validate summary generation from conversation context upon session pause or stop.
- Developed integration tests to cover the full observation lifecycle, including context injection, observation queuing, and error recovery.
- Introduced reusable mock factories and scenarios for consistent testing across different test files.

vitest.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    globals: true,
+    include: ['tests/**/*.test.ts'],
+    exclude: [
+      '**/node_modules/**',
+      '**/dist/**',
+      // Exclude node:test format files (they use node's native test runner)
+      'tests/strip-memory-tags.test.ts',
+      'tests/user-prompt-tag-stripping.test.ts'
+    ],
+  },
+});