test: isolate ozone test directories

[setchy]

Summary

• Replace the shared /tmp/gitify-test-userdata path with a unique fs.mkdtempSync directory under os.tmpdir() for each test.
• Point the Electron userData mock at that test's directory and derive its marker path from the same location.
• Restore spies/platform state and remove only the directory created for that test during teardown, avoiding shared marker files and leftover directories.

Addresses the two sonarjs/publicly-writable-directories findings from the one-off test-code scan while improving test isolation. Only src/main/ozone.test.ts changes; no production Ozone behavior, dependencies, or configuration changes.

Validation

• Focused Ozone suite: 9 tests passed.
• Full suite: 1,865 tests passed across 186 files.
• TypeScript, formatting/lint checks, and production build passed. The build emitted a non-fatal chunk-size warning.
• Type-aware SonarJS recommended-rule scan of the changed file: zero findings and zero parsing errors. This is a local ESLint-plugin result, not a claim about SonarCloud issue closure.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud