Add NextReset to productivity tools

[poirot1226]

Adds NextReset in the existing list format. It is a free, working resource for Codex users that records observed reset history, links official incident sources, and includes a browser-local personal timer.

Limits: it is independent and unofficial; historical observations do not guarantee future reset timing. I am submitting this listing on behalf of the NextReset project.

[CLAassistant]

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