Every chip on the home feed filters the timeline or is not drawn, and a test presses each one #5801

Part of #5735. The owner reports that the Pull requests/decisions, crew words, releases and agents buttons do nothing.

Done when:

• [ ] Reproduce it first. On production / as the owner, write down which chips change nothing and why, and put that in the pull description.
• [ ] A chip with no posts to filter is not drawn. A drawn chip shows its count (Releases 3). A chip the viewer switched off stays, so it can be switched back on.
• [ ] Posts the asks list pulls out of the timeline still count for, and show under, their chip. Or the chip says it filters the asks too. Pressing it always changes what is visible.
• [ ] test/feed-chips.test.ts presses every drawn chip on a seeded home and checks that the visible posts change.
• [ ] MCP feed_chips gives the same chips and counts.

Files: src/feed/chips.ts, src/web/studio/feed.ts, src/http/mcp.ts, test/feed-chips.test.ts.

Replaced by #6849. Parked twice: the reviews asked to count chips from the 20 posts the page draws, with no second feed rank, and to leave out asks the home doesn't draw. #6849 states that as done.