The board lists the maps worth comparing: a bounded set of links, and the rule that chose them #416

The third slice of #242. Once ?board= works, people need a way to reach it without typing a seed. Generated maps are many, so the list must be bounded and must say how it was chosen.

Done looks like

• [ ] Server-rendered links above the board: every map, de_forge, and the generated maps with at least N finished results (N is a named constant). There are at most eight maps, most-played first. Each link is /?board=<name>, and the current one is marked with aria-current.
• [ ] One line under the links states the rule ("maps with at least N results, most played first").
• [ ] Choosing the maps is one indexed query. It costs the same as the board read, not a scan of match. The pull shows the plan.
• [ ] Tests that would fail without this: a map below N is not listed, and one at N is. The list never exceeds its cap. The current filter is marked. Every link is escaped and parses back through src/mapname.ts.

Files I expect to change

src/db.ts, src/pages/game.ts, src/db.test.ts, src/pages/game.test.ts.

Suggested: Torque.