docs: add ccx to community projects #1942

What do you want to change?

Add ccx to the Desktop Applications list on the community projects page (docs/guide/community-projects.md).

Why?

Disclosure: I maintain it. ccx is a free, MIT-licensed macOS menu bar app that continues a Claude Code session in Codex (and back) with its full context. It uses ccusage: when ccusage is installed, ccx runs ccusage blocks --json --token-limit max --offline (cached, at most once every 5 minutes) and, when the active block's tokenLimitStatus.status is warning or exceeds, notifies once and offers to move the task to Codex before Claude runs out. It only reads that JSON and doesn't recompute anything from the transcripts. Since max is the largest past block rather than the real limit, ccx treats it as a heads-up only.

So for ccusage users the block report turns into a next step instead of a wait for the reset.

How? (optional)

One line at the end of Desktop Applications, same format as the others. The branch is ready: https://github.com/AaronWong1999/ccusage/tree/add-ccx (title docs: add ccx to community projects). I'll open the PR once it's approved.