fuzzy-match + recency-rank the command palette

Completes the command-palette acceptance: the filter is now a
subsequence fuzzy match (was substring), and recently-invoked commands
float to the top and break score ties. The subsequence matcher is
extracted to a shared fuzzy helper so the palette and quick-open file
finder use one implementation instead of a private copy each.

Pinned commands and cross-session recency persistence are left as a
follow-up (they need a pin affordance + settings storage).

Co-Authored-By: Claude <noreply@anthropic.com>

test/kernel/src/fuzzy_test.dart

@@ -0,0 +1,35 @@
+import 'package:clide/kernel/src/fuzzy.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('fuzzyScore', () {
+    test('empty query scores 0 (matches anything)', () {
+      expect(fuzzyScore('anything', ''), 0);
+    });
+
+    test('returns null when query is not a subsequence', () {
+      expect(fuzzyScore('git commit', 'xyz'), isNull);
+      expect(fuzzyScore('abc', 'abcd'), isNull); // query longer / extra char
+    });
+
+    test('matches non-contiguous subsequences', () {
+      expect(fuzzyScore('git commit', 'gc'), isNotNull);
+      expect(fuzzyScore('theme pick', 'tp'), isNotNull);
+    });
+
+    test('lower score is better: contiguous + early beats gappy + late', () {
+      final contiguousEarly = fuzzyScore('abcxxxx', 'abc')!; // match at 0,1,2
+      final gappyLate = fuzzyScore('xxxxabc', 'abc')!; // starts at 4
+      expect(contiguousEarly, lessThan(gappyLate));
+
+      final tight = fuzzyScore('ab', 'ab')!; // adjacent
+      final spread = fuzzyScore('axb', 'ab')!; // a gap between a and b
+      expect(tight, lessThan(spread));
+    });
+
+    test('case sensitivity is the caller\'s responsibility', () {
+      expect(fuzzyScore('GIT', 'git'), isNull); // differing case → no match
+      expect(fuzzyScore('GIT'.toLowerCase(), 'git'), isNotNull);
+    });
+  });
+}