fix(ingest): read an open range written in slash dates

`parseOpenRange` only ever read a month-name start, because it delegates to
`parseMonthDayYear`. So `Jul. 24, 2026 - End of 4.6` parsed and
`09/02/2026 - TBA` did not.

Game8 re-cut Endfield's upcoming table from version 1.4 to 1.5 and wrote the
whole new schedule in the second notation. All nine rows became undatable and
were dropped in silence: the source went from one event to zero, the parse gate
kept the previous snapshot, and the run reported a shape change on a page whose
shape had not changed. Nine announced events were invisible with no error
anywhere — the failure § Working on parsers calls the dangerous one.

Which notation a page uses is house style, not a statement about how certain the
source is, so both are read. The year stays mandatory in either: this is the
last reader tried, so nothing downstream would catch a guess, and Game8's
year-less summary rows (`08/12 - 08/24`) must keep returning null rather than
becoming confidently dated events.

The two-digit year pivot moves out of `parseShortSlashRange` into `pivotYear`
rather than being written a second time.

Diffed across every pinned fixture and all nineteen live snapshots: no event
moved.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

test/dates.test.ts

@@ -144,6 +144,21 @@ describe("parseOpenRange", () => {
     }
   });
 
+  test("keeps a slash-dated start when the end is not a date", () => {
+    // Game8 schedules a version before it announces the ends: Endfield's
+    // upcoming table reads "Period: 09/02/2026 - TBA". That is the same honest
+    // unknown as "End of 4.6", written in slashes instead of month names, and
+    // dropping the row makes nine announced events vanish with no error.
+    expect(parseOpenRange("09/02/2026 - TBA")).toEqual({
+      start: { iso: "2026-09-02T00:00:00.000Z", precision: "day" },
+      end: null,
+    });
+    expect(parseOpenRange("09/09/26 - TBA")).toEqual({
+      start: { iso: "2026-09-09T00:00:00.000Z", precision: "day" },
+      end: null,
+    });
+  });
+
   test("returns null when there is no full date at all", () => {
     expect(parseOpenRange("08/12 - 08/24")).toBeNull();
     expect(parseOpenRange("Releases in Version 3.6")).toBeNull();