refactor(04): move rank.test.ts into tests/ mirror dir (convention + dist hygiene)

src/lib/rank.test.ts was the last co-located API test. The API tsconfig excludes
tests/ from the build, so all test files belong there; a test in src/ gets compiled
into dist/ and vitest then runs the stale compiled copy (the source of phantom
'22 todo' and dist sourcemap warnings). Moving it to tests/lib/ matches convention
and leaves zero test files in src/, so the production build no longer emits test
artifacts. Updated rank.test.ts path refs in phase-04 plan docs.

.planning/phases/04-shared-lists-live-sync/04-05-PLAN.md

@@ -8,7 +8,7 @@ files_modified:
   - apps/pwa/src/routes/ListDetail.tsx
   - apps/pwa/src/components/ItemRow.tsx
   - apps/pwa/src/api/listsClient.ts
-  - apps/api/src/lib/rank.test.ts
+  - apps/api/tests/lib/rank.test.ts
   - apps/api/tests/routes/lists.test.ts
 autonomous: true
 requirements: [LIST-03]
@@ -97,9 +97,9 @@ Output: dnd-kit DndContext/SortableContext in ListDetail; sortable ItemRow with
 
 <task type="auto">
   <name>Task 2: Strengthen server-side reorder ordering tests (LIST-03, D-13)</name>
-  <files>apps/api/src/lib/rank.test.ts, apps/api/tests/routes/lists.test.ts</files>
+  <files>apps/api/tests/lib/rank.test.ts, apps/api/tests/routes/lists.test.ts</files>
   <read_first>
-    - apps/api/src/lib/rank.test.ts (from Plan 04)
+    - apps/api/tests/lib/rank.test.ts (from Plan 04)
     - apps/api/tests/routes/lists.test.ts (PATCH position coverage)
     - .planning/phases/04-shared-lists-live-sync/04-VALIDATION.md (LIST-03 row: "PATCH new rank produces correct fractional order")
     - .planning/phases/04-shared-lists-live-sync/04-RESEARCH.md §"Common Pitfalls" Pitfall 2 (precision)
@@ -108,7 +108,7 @@ Output: dnd-kit DndContext/SortableContext in ListDetail; sortable ItemRow with
     Add server-side tests proving reorder correctness: (a) repeated mid-point inserts via rankBetween produce strictly increasing distinct strings over many iterations (precision does not collapse — Pitfall 2); (b) PATCH /api/list-items/:id { position } updates only rank and a subsequent GET returns items in the new ASC order; (c) moving an item between two neighbors yields a rank strictly between theirs. These align the LIST-03 row in 04-VALIDATION.md to a green automated check. No production behavior change — Plan 04 already implements the PATCH position path.
   </action>
   <verify>
-    <automated>pnpm --filter @familysync/api exec vitest run src/lib/rank.test.ts tests/routes/lists.test.ts</automated>
+    <automated>pnpm --filter @familysync/api exec vitest run tests/lib/rank.test.ts tests/routes/lists.test.ts</automated>
   </verify>
   <acceptance_criteria>
     - LIST-03 ordering test ("PATCH new rank produces correct fractional order") is present and green.
@@ -136,7 +136,7 @@ Output: dnd-kit DndContext/SortableContext in ListDetail; sortable ItemRow with
 </threat_model>
 
 <verification>
-<automated>pnpm --filter @familysync/api exec vitest run src/lib/rank.test.ts tests/routes/lists.test.ts && pnpm --filter @familysync/pwa exec tsc --noEmit</automated>
+<automated>pnpm --filter @familysync/api exec vitest run tests/lib/rank.test.ts tests/routes/lists.test.ts && pnpm --filter @familysync/pwa exec tsc --noEmit</automated>
 - `playwright-cli`: drag-reorder persists across reload.
 </verification>