Do new example blocks need hidden: true? Rule says yes, all 630 existing blocks say no

**Decision needed:** should new doc site example blocks be `hidden: true` at first, or not?

**The conflict.** `.github/instructions/templates.instructions.md` says to flag any new block whose `.doc.mjs` is not `hidden: true`. But **0 of 630** existing component blocks are hidden. Every one shipped visible.

So either the rule means page templates only, or 630 blocks broke it.

**Why it matters now.** PR #5203 adds `BottomSheetSnapPoints`, a new block. I made it visible to match the other 630. If the rule was meant to apply, that PR needs a one-line change.

**What to do:** pick one.
- **A — rule is for page templates.** Edit the instructions to say so. #5203 is fine as-is.
- **B — rule covers blocks too.** Add `hidden: true` to the new block in #5203. The other 630 are pre-existing debt.

Either answer is quick. The point is that reviewers keep hitting this and there is no written answer.

_Filed from #5203, where a reviewer note would have gone unread._

Read .github/instructions/templates.instructions.md and compare its hidden: true rule with the 630 existing component blocks described in the issue. Review PR #5203 and its BottomSheetSnapPoints block, then document whether the rule applies to blocks or page templates and update the instruction or PR accordingly.

Written by the indexing model from the issue text.