chore(ci): clear the lint debt and make lint blocking (#79)

CI ran lint with continue-on-error because 23 errors predated it. All are
fixed, so the flag is gone and a typecheck step is added beside it — nothing
else in CI compiles the test files, so a type error in a fixture could only
ever be found on a developer's machine.

Real fixes, no blanket disables and no suppressions:

- react-hooks/set-state-in-effect (6): each was "reset or seed state when an
  input changes", so each becomes a state adjustment during render behind a
  previous-value guard — the documented React pattern for it. Two were also
  latent bugs. transactions/page.tsx depended on `others`, rebuilt by .filter()
  every render, so the effect already ran every render, one commit late.
  shared/page.tsx depended on the `tagIds` array identity, so the row window
  was reset more often than "changing any filter" claims — including after
  "Show more", the one interaction it must not undo; the key now joins by
  value. csv-import-modal reads localStorage once at mount, which is a lazy
  useState initializer, not an effect (SSR-guarded, though the modal is
  mounted from client state and never prerenders).
- react-hooks/static-components (3): SortIcon was declared inside SharedPage,
  making it a new component type on every render. Hoisted to module scope with
  the sort state passed as props.
- @typescript-eslint/no-explicit-any (9): the dynamically imported route
  handlers in two integration tests. Typed as their real signatures with one
  `as unknown as NextRequest` cast at the fixture boundary, so the call sites
  and response bodies get checked instead of opted out.
- react/no-unescaped-entities (5): exact-equivalent entities (', "),
  so no rendered text changes.

Also fixes the one pre-existing tsc error (unit/order-ingestion.test.ts:511):
`options` is optional, and `?? 0` keeps the assertion failing on an absent
list rather than silencing it with a non-null bang.

9 warnings remain (no-unused-vars, exhaustive-deps). eslint exits 0 on
warnings, so lint blocks on errors only — deliberately, since none of the
remaining warnings should stop a push.

src/app/shared/page.tsx

@@ -432,6 +432,19 @@ const SharedTxRow = memo(function SharedTxRow({
 // ── Main page ─────────────────────────────────────────────────────────────────
 type SortCol = "transaction_date" | "created_at" | "amount";
 
+/**
+ * Sort direction marker for a column header.
+ *
+ * Declared at module scope and given the sort state as props, rather than
+ * closing over it inside SharedPage: a component defined during render is a
+ * new type on every render, so React unmounts and remounts it each time
+ * instead of updating it.
+ */
+function SortIcon({ col, sortCol, sortDir }: { col: SortCol; sortCol: SortCol; sortDir: "asc" | "desc" }) {
+  if (sortCol !== col) return <span className="text-zinc-600 ml-0.5">↕</span>;
+  return <span className="ml-0.5">{sortDir === "desc" ? "↓" : "↑"}</span>;
+}
+
 export default function SharedPage() {
   const [tagIds, setTagIds] = useState<string[]>([]);
   const [participantId, setParticipantId] = useState<number | undefined>(undefined);
@@ -478,10 +491,6 @@ export default function SharedPage() {
     else { setSortCol(col); setSortDir("desc"); }
   }
 
-  function SortIcon({ col }: { col: SortCol }) {
-    if (sortCol !== col) return <span className="text-zinc-600 ml-0.5">↕</span>;
-    return <span className="ml-0.5">{sortDir === "desc" ? "↓" : "↑"}</span>;
-  }
   const { data: balances = [], isLoading: balLoading } = useParticipantBalances(realTagIds);
   const { data: allTags = [] } = useTags();
   const { data: me } = useCurrentUser();
@@ -504,9 +513,17 @@ export default function SharedPage() {
   // table was what made expanding a receipt freeze the browser. "Show more"
   // extends the window; changing any filter resets it.
   const [visibleCount, setVisibleCount] = useState(100);
-  useEffect(() => {
+  // Reset during render behind a previous-value guard rather than in an effect.
+  // Note the key joins `tagIds` by value: as a raw dependency it was a fresh
+  // array on many renders, so the window was being reset more often than
+  // "changing any filter" claims — including after "Show more", which is the
+  // one interaction this must not undo.
+  const windowKey = `${search}|${sortCol}|${sortDir}|${tagIds.join(",")}|${participantId ?? ""}`;
+  const [lastWindowKey, setLastWindowKey] = useState(windowKey);
+  if (windowKey !== lastWindowKey) {
+    setLastWindowKey(windowKey);
     setVisibleCount(100);
-  }, [search, sortCol, sortDir, tagIds, participantId]);
+  }
   const visible = (transactions as SharedTransactionRow[]).slice(0, visibleCount);
 
   // Receipt expansion, same pattern as the transactions page. The shared
@@ -667,13 +684,13 @@ export default function SharedPage() {
                   className="text-left px-4 py-2 text-xs text-zinc-500 font-medium cursor-pointer hover:text-white whitespace-nowrap"
                   onClick={() => toggleSort("transaction_date")}
                 >
-                  Date <SortIcon col="transaction_date" />
+                  Date <SortIcon col="transaction_date" sortCol={sortCol} sortDir={sortDir} />
                 </th>
                 <th
                   className="text-left px-4 py-2 text-xs text-zinc-500 font-medium cursor-pointer hover:text-white whitespace-nowrap"
                   onClick={() => toggleSort("created_at")}
                 >
-                  Imported <SortIcon col="created_at" />
+                  Imported <SortIcon col="created_at" sortCol={sortCol} sortDir={sortDir} />
                 </th>
                 <th className="text-left px-4 py-2 text-xs text-zinc-500 font-medium sticky left-0 z-10 bg-zinc-900 border-r border-zinc-800/80">Description</th>
                 <th className="text-left px-4 py-2 text-xs text-zinc-500 font-medium">Category</th>
@@ -681,7 +698,7 @@ export default function SharedPage() {
                   className="text-right px-4 py-2 text-xs text-zinc-500 font-medium cursor-pointer hover:text-white"
                   onClick={() => toggleSort("amount")}
                 >
-                  Amount <SortIcon col="amount" />
+                  Amount <SortIcon col="amount" sortCol={sortCol} sortDir={sortDir} />
                 </th>
                 {/* Paid by sits next to Splits deliberately: together they are the
                     two halves of the question this page exists to answer — whose