chore(events): remove dead UPDATE_THEME event and onSystemThemeUpdate API

[afonsojramos]

Summary

EVENTS.UPDATE_THEME and the window.gitify.onSystemThemeUpdate registration shim are dead code:

• No code in src/main/ ever calls sendRendererEvent(mb, EVENTS.UPDATE_THEME, …) — there is no producer.
• No code in src/renderer/ ever calls window.gitify.onSystemThemeUpdate(…) — there is no consumer.
• Only the registration plumbing and its test exist, plus a vi.fn() stub in the renderer test setup.

Theme handling currently happens entirely on the renderer side via @primer/react's useTheme and the OS-level prefers-color-scheme media query. The IPC channel was never wired up.

Removed

• EVENTS.UPDATE_THEME and its EventContracts entry.
• window.gitify.onSystemThemeUpdate from src/preload/index.ts.
• The corresponding test in src/preload/index.test.ts.
• The onSystemThemeUpdate mock from the renderer test setup.

Verified

pnpm tsc --noEmit clean, pnpm test 937/937, pnpm lint:check 0 errors.

If OS theme tracking is wanted in future, the right shape is nativeTheme.on('updated', …) on the main side, not this listener-without-a-producer.

[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

[setchy]

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