style(frontend): document the four one-shot setState-in-effect sites

eslint-plugin-react-hooks v7 flags setState inside an effect body. All four
occurrences predate this refactor and are one-shot initialisation or external
sync, not the cascading-render pattern the rule targets:

  - hydrating a ?q= deep link once the database is ready
  - reading the candidate count for the footer
  - auto-running the schema preset when the SQL tab first opens
  - mirroring the parent-owned query into SearchForm for deep links and clear

Each gets a scoped disable with a comment explaining why it is correct here,
rather than a blanket rule change. Restructuring these properly would mean
reworking deep-link hydration and auto-search with no test harness to catch a
regression; that is worth doing separately, not inside this refactor.

npm run lint is now clean.

src/App.jsx

@@ -98,17 +98,21 @@ function DatasetApp({ dataset }) {
     [db],
   );
 
-  // Run initial URL query once DB is ready
+  // Hydrate a ?q= deep link once, as soon as the database is ready. Fires at
+  // most once per mount, so it cannot cascade.
   useEffect(() => {
+    // eslint-disable-next-line react-hooks/set-state-in-effect
     if (db && query) handleSearch(query);
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [db]);
 
-  // Fetch total count for footer once DB loads
+  // Read the candidate count for the footer once the database loads. One-shot
+  // per mount; the query result cannot change without a new database.
   useEffect(() => {
     if (!db) return;
     const stmt = db.prepare("SELECT COUNT(*) AS c FROM student");
     stmt.step();
+    // eslint-disable-next-line react-hooks/set-state-in-effect
     setTotalCount(stmt.getAsObject().c);
     stmt.free();
   }, [db]);

src/components/custom-query.jsx

@@ -82,6 +82,7 @@ export function CustomQuery({ db, disabled, presets = [] }) {
   // sees the student columns instead of a blank textarea.
   useEffect(() => {
     if (db && schemaPreset && columns.length === 0 && !sql) {
+      // eslint-disable-next-line react-hooks/set-state-in-effect
       executeQuery(schemaPreset.sql);
       setSql(schemaPreset.sql);
     }

src/components/search-form.jsx

@@ -16,8 +16,11 @@ export function SearchForm({
   const { mode, hint } = detectMode(query);
   const canSearch = mode === "sbd" || mode === "name";
 
-  // Sync from external value (deep-link URL, clear button in parent)
+  // Mirror the parent's query into local state. The parent owns the value so
+  // it can bind it to the URL; this only runs when that external value changes
+  // (deep-link hydration, or the clear button), never in response to typing.
   useEffect(() => {
+    // eslint-disable-next-line react-hooks/set-state-in-effect
     setQuery(value);
   }, [value]);