Spec #136: finished becomes a Series fact, Lane gate rewritten on it (#157)

finished_at lands on series (0016 seeds it from the pre-flip finished
bookmarks, then flips those bookmarks to archived), the poll gate and
eligible count read the flag instead of a per-Reader vote, PUT rejects
the finished status like any unknown value, and the web UI drops the
Finished tab, badge and finish button. Novel merge rank is archived >
reading. Per-Reader disagreement (one Reader keeps a finished Series in
reading forever) is what the flag repairs; the cutover keeps polling
state unchanged for every Series.

userscript/test/logic.test.js

@@ -395,7 +395,6 @@ test("statusOf defaults a missing status to reading", () => {
   assert.equal(statusOf({}), "reading");
   assert.equal(statusOf({ status: "" }), "reading");
   assert.equal(statusOf({ status: "archived" }), "archived");
-  assert.equal(statusOf({ status: "finished" }), "finished");
 });
 
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