Fix deterministic theme initial render

[konard]

Summary

• Make the root theme state deterministic on the first render by defaulting to light.
• Apply the saved localStorage theme after mount instead of during the initial state initializer.
• Add a regression test that prevents localStorage reads from returning to the initial render path.

Reproduction

The reported React minified errors #418 and #423 are hydration mismatch/recovery errors. The root app could render different markup on the first client render depending on localStorage theme state, because ThemeProvider read localStorage inside the useState initializer.

Verification

• npm test
• npm run build

Fixes #112

[konard]

Solution summary

Implemented and pushed the fix to issue-112-612890af4be9.

Root cause addressed: ThemeProvider was reading localStorage during the initial useState render, making the first client render depend on browser state. That can trigger React hydration mismatch/recovery errors like #418 and #423. The provider now starts deterministically with light and applies the stored theme after mount.

Added regression coverage in tests/theme-initial-render.test.mjs.

Verification passed:

• npm test
• npm run build

PR 113 is updated and marked ready for review: #113

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[konard]

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[konard]

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