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/components/rule-preview-modal.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useEffect, useMemo, useState } from "react";
+import { useMemo, useState } from "react";
 import { useRuleMatches, useApplyRuleToSelection, type RuleMatchChange } from "@/lib/hooks";
 import { formatCategory } from "@/lib/categories";
 
@@ -39,9 +39,17 @@ export function RulePreviewModal({
 
   // Default to everything the rule would change — the common case is "yes, all
   // of these", with deselection as the exception.
-  useEffect(() => {
-    if (data?.transactions) setSelected(new Set(data.transactions.map((t) => t.id)));
-  }, [data]);
+  //
+  // Adjusted during render behind a previous-value guard rather than in an
+  // effect. In an effect the modal painted once with nothing ticked and then
+  // again with everything ticked; here the seeded selection is part of the
+  // first commit. The guard is on `data` identity, so a user deselecting a row
+  // is not undone on the next render — only a genuinely new preview reseeds.
+  const [seededFrom, setSeededFrom] = useState<typeof data>(undefined);
+  if (data !== seededFrom) {
+    setSeededFrom(data);
+    setSelected(new Set(data?.transactions?.map((t) => t.id) ?? []));
+  }
 
   const rows = data?.transactions ?? [];
   const allSelected = rows.length > 0 && selected.size === rows.length;