refactor: delete gemini.test.ts, move signal/TTY tests to cleanup.test.ts

Addresses review feedback: removed the new gemini.test.ts file and moved
signal handler and TTY check tests into cleanup.test.ts where they belong.
Reverted the eslint allowDefaultProject workaround since deleting the .ts
file eliminates the stem conflict.

Author: yuvrajangadsingh

eslint.config.js

@@ -86,13 +86,7 @@ export default tseslint.config(
     languageOptions: {
       parser: tseslint.parser,
       parserOptions: {
-        projectService: {
-          allowDefaultProject: [
-            // gemini.test.tsx shares its stem with gemini.test.ts, so TS
-            // project service resolves the .ts and skips the .tsx variant.
-            'packages/cli/src/gemini.test.tsx',
-          ],
-        },
+        projectService: true,
         tsconfigRootDir: projectRoot,
       },
       globals: {