diigo-cache: diigo counts pages from 0; migrate stored pages (schema v2)

Comparing a cache with diigo's RSS export: the size-100 walk had missed
exactly the 100 newest bookmarks (everything updated since 2026-09-16).
diigo's page_num is 0-based, and we sent our 1-based page number
unchanged, so "page 1" was really page 2 and the newest page was never
fetched. diigo's total (16744) was right; the "total-overstated"
reading was a misdiagnosis.

- page() asks for page_num = n - 1
- BREAKING for stored state, agreed beforehand, migrated in place:
  schema v2 renumbers every stored page +1 (pages and page_members, via
  negation so no number collides), once, recorded as kv "schema" = 2;
  nothing is refetched, page 1 just becomes a miss
- fill jobs record their numbering; a job saved without it fails ("page
  numbering changed …; start the fill again") instead of resuming
- the fake pages from 0 like diigo (7 tests failed until the fix);
  tests feed v1-shaped storage and a v1-numbered job to the new code
- the next-page peek guard stays; its comments no longer claim diigo
  overstates its total
- the fixed test clock moves to 2099: pinned to "today" its alarms came
  due in real time and fired on their own

Generated-by: Claude Opus 5.5

diigo-cache/tests/fill.test.ts

@@ -131,7 +131,7 @@ describe("fill job (goal 1e)", () => {
 		expect(status?.error).toMatch(/page size not honored/);
 	});
 
-	it("fills to the real end when diigo's total overstates its items", async () => {
+	it("fills to the real end if a total overstates the items", async () => {
 		const stub = await wired("fake-overstated-webapp");
 		await stub.startFill();
 		await drain(stub);
@@ -143,6 +143,18 @@ describe("fill job (goal 1e)", () => {
 		expect((await stub.page(3, PAGE_SIZE)).items).toHaveLength(50);
 	});
 
+	it("a job saved under the old page numbering fails instead of resuming", async () => {
+		const stub = await wired();
+		await runInDurableObject(stub, async (_obj, state) => {
+			const at = new Date().toISOString();
+			await state.storage.put("fill", { state: "running", nextPage: 40, pages: 168, fetched: 39, pageSize: 100, startedAt: at, updatedAt: at });
+			await state.storage.setAlarm(Date.now() + 60_000);
+		});
+		await drain(stub);
+		expect((await stub.fillStatus())?.error).toMatch(/page numbering changed/);
+		expect(await stub.startFill()).toMatchObject({ state: "running", nextPage: 1, numbering: 2 });
+	});
+
 	it("a job saved under another page size fails instead of resuming; a new start replaces it", async () => {
 		const stub = await wired();
 		// the shape a 24-per-page job left in storage (no pageSize field)