fix: clamp displayed month when endMonth changes

[wanxiankai]

Summary

• Clamp the internally displayed month when navigation bounds change after mount.
• Keep dropdown captions and the month grid visible when a new endMonth falls before the current month.
• Add a regression test for issue Changing endMonth to a date smaller than the currently viewed month removes the month grid and dropdowns #2912.

Fixes #2912

Tests

• pnpm exec jest packages/react-day-picker/src/DayPicker.test.tsx --selectProjects src --runInBand --no-watchman
• pnpm run lint
• pnpm run typecheck
• TZ=UTC pnpm exec jest --selectProjects examples --selectProjects src --selectProjects packages --selectProjects scripts --runInBand --no-watchman

[changeset-bot]

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Latest commit: 2e584ae

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