Add spoiler tags to protect sensitive content

Cove Collective is an infertility support community. Our members are at different stages of treatment and have varying emotional capacities on any given day. Spoiler tags (using || syntax as seen on Reddit and Discord) would allow users to voluntarily hide sensitive content behind a click to reveal. This is standard functionality in similar community-based platforms, and is really core infrastructure that would make Heartbeat meaningfully more suitable for sensitive topic peer communities (infertility, grief, mental health, chronic illness).