refactor: address review — helper-built paths and a fuller grep hint

Three of the five review comments were correct:

- `provider_initializer.dart` built festival-root paths by interpolating
  `'/${provider.currentFestival.id}'` directly. AGENTS.md requires the typed
  helpers, so both sites now go through `buildFestivalHome()`. Output is
  identical; the helper adds a non-empty assert.
- The `analyze` grep hint still suggested `error\|warning`, which now hides
  the info-severity findings that fail the task. Widened to
  `grep -nE 'info|warning|error'`.

This means the moved widgets are no longer byte-identical to the originals
as claimed in the PR description; the two `router.go` call sites are the
only difference.

The other two comments claimed `'key': ?value` is invalid Dart. It is a
null-aware map entry, stable since 3.9 (this package requires >=3.10.0), and
is what the now-fatal `use_null_aware_elements` lint asked for — reverting
would fail `analyze`. Refuted on the threads.

Refs #524, #527

Author: claude

lib/widgets/provider_initializer.dart

@@ -94,7 +94,7 @@ class _ProviderInitializerState extends State<ProviderInitializer>
 
       // Check if we're on root path - redirect to festival home
       if (currentPath == '/') {
-        router.go('/${provider.currentFestival.id}');
+        router.go(buildFestivalHome(provider.currentFestival.id));
         return;
       }
 
@@ -134,7 +134,8 @@ class _ProviderInitializerState extends State<ProviderInitializer>
         final queryString = currentUri.query.isNotEmpty
             ? '?${currentUri.query}'
             : '';
-        router.go('/${provider.currentFestival.id}$restOfPath$queryString');
+        final festivalHome = buildFestivalHome(provider.currentFestival.id);
+        router.go('$festivalHome$restOfPath$queryString');
       }
     } catch (e, stackTrace) {
       if (kDebugMode) {

mise-tasks/analyze.sh

@@ -10,5 +10,5 @@ flutter analyze "$@" 2>&1 |
 	tee "$ANALYZE_LOG"
 EXIT_CODE=${PIPESTATUS[0]}
 echo "---"
-echo "Grep with: grep -n 'error\|warning' $ANALYZE_LOG"
+echo "Grep with: grep -nE 'info|warning|error' $ANALYZE_LOG"
 exit "$EXIT_CODE"