test(tally): add 4 tests for --regex/-r path covering SC #1, #2, #4, #5

Step 4 (final) of plan.md (Spor B B3 pipeline run). Adds 4 new tests
in a contiguous block at the end of tests/tally.test.mjs, mirroring
the existing spawnSync style. All 4 test names contain --regex or -r.

Coverage map:
- SC #1 (long form, exit 0): test 1
- SC #2 (-r short form): test 2
- SC #4 (invalid exits 2 with /^tally: invalid regex/): test 3
- SC #5 (--json includes flags.regex): test 4

Total: 14 tests, all green, 3.16s wall-clock (under 5s cap).

[skip-docs]

plugins/ultraplan-local/examples/02-real-cli/tests/tally.test.mjs

@@ -91,3 +91,37 @@ test('--help: stdout contains "Usage:", exit 0', () => {
   assert.match(r.stdout, /Usage:/);
   assert.match(r.stdout, /--ignore-case/);
 });
+
+// --- Tests for --regex / -r mode (added in plan step 4, Spor B B3) ---
+
+test("--regex 'fo+' counts more matches than literal 'foo' (long form, exit 0)", () => {
+  const literal = run('foo', SAMPLE);
+  const regex = run('--regex', 'fo+', SAMPLE);
+  assert.equal(literal.status, 0);
+  assert.equal(regex.status, 0);
+  assert.ok(Number(regex.stdout) >= Number(literal.stdout),
+    `regex count (${regex.stdout.trim()}) should be >= literal count (${literal.stdout.trim()})`);
+});
+
+test("-r short form equals --regex long form (same stdout)", () => {
+  const short = run('-r', 'fo+', SAMPLE);
+  const long = run('--regex', 'fo+', SAMPLE);
+  assert.equal(short.status, 0);
+  assert.equal(long.status, 0);
+  assert.equal(short.stdout, long.stdout);
+});
+
+test("--regex '[' exits 2 with stderr 'tally: invalid regex'", () => {
+  const r = run('--regex', '[', SAMPLE);
+  assert.equal(r.status, 2);
+  assert.equal(r.stdout, '');
+  assert.match(r.stderr, /^tally: invalid regex/);
+});
+
+test("--json --regex 'fo+' includes flags.regex === true in output", () => {
+  const r = run('--json', '--regex', 'fo+', SAMPLE);
+  assert.equal(r.status, 0);
+  const parsed = JSON.parse(r.stdout);
+  assert.equal(parsed.flags.regex, true);
+  assert.ok(typeof parsed.count === 'number' && parsed.count > 0);
+});