A repository's upstream-follow card shows its last five checks: when, how far behind, and what happened #5979

A fork that follows its upstream should show its record, not only the last word.

Done when:

• [ ] Each follow check (src/actions/upstream_follow.ts noteCheck) is also appended to a small history table in the forge's sqlite, keeping the last 20 per repository.
• [ ] The card (src/web/pages/upstream-follow.ts) lists the last 5: 2 h ago · 3 behind · merged, · conflict in N files, or · error: <first line>.
• [ ] The migration is additive. A repository with no history shows only today's line.
• [ ] Tests: 25 checks keep 20 and show 5, newest first, with each outcome worded. Do not touch src/http/mcp.ts, src/contract/openapi.ts or docs/DESIGN.md.