Ux/rename threads to contexts

[adamleithp]

Problem

Name channels is confusing

Changes

Surface level rename from Channels => Contexts

How did you test this?

locally

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[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit acc71f6.}

[greptile-apps]

_{Reviews (1): Last reviewed commit: "Rename channels to contexts" | Re-trigger Greptile}

[github-actions]

Pure UI rename of "channels/threads" to "contexts": label text, icon swap (HashIcon → SquircleDashed from an existing dependency), removal of # prefixes, and corresponding test updates. No data model, API contract, or business logic is affected.