fix: filter presence read paths by per-post capability

[josephfusco]

#128 scoped the gap as REST-only, so #158 closed the REST path while the Active Posts widget and the admin bar kept serving post titles, edit links and editor names for every room to anyone with edit_posts.

Closes #128

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5
Used for: Drafting and implementation

[github-actions]

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[github-actions]

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