fix: replace invalid \Z regex anchor and remove redundant pattern

The original PR (#1337) used \Z in a JavaScript regex, which is a
Perl/Python/Ruby anchor — JavaScript interprets it as a literal match
for the character 'Z', silently truncating expected text containing
that letter. Replace with a two-pass approach: try next-key lookahead
first, fall back to greedy match to end-of-string.

Also remove the redundant `to=all:` pattern in sanitizeForDisplay()
since it is a subset of the existing `to=[^:\s]+:` pattern.

Add regression tests proving the Z-truncation bug and verifying
expected blocks at end-of-section parse correctly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/uat.test.cjs

@@ -390,6 +390,51 @@ awaiting: user response
     assert.ok(result.output.includes('Chinese strings render correctly.'));
   });
 
+  test('does not truncate expected text containing the letter Z', () => {
+    fs.writeFileSync(uatPath, `---
+status: testing
+phase: 01-test-phase
+---
+
+## Current Test
+
+number: 3
+name: Timezone display
+expected: |
+  Timezone abbreviation shows CET.
+  Zero-offset zones display correctly.
+awaiting: user response
+`);
+
+    const result = runGsdTools(['uat', 'render-checkpoint', '--file', '.planning/phases/01-test-phase/01-UAT.md', '--raw'], tmpDir);
+    assert.strictEqual(result.success, true, `render-checkpoint failed: ${result.error}`);
+    assert.ok(result.output.includes('Timezone abbreviation shows CET.'),
+      'Expected text before Z-containing word should be present');
+    assert.ok(result.output.includes('Zero-offset zones display correctly.'),
+      'Expected text starting with Z should not be truncated by \\Z regex bug');
+  });
+
+  test('parses expected block when it is the last field in the section', () => {
+    fs.writeFileSync(uatPath, `---
+status: testing
+phase: 01-test-phase
+---
+
+## Current Test
+
+number: 4
+name: Final field test
+expected: |
+  This block has no trailing YAML key.
+  It ends at the section boundary.
+`);
+
+    const result = runGsdTools(['uat', 'render-checkpoint', '--file', '.planning/phases/01-test-phase/01-UAT.md', '--raw'], tmpDir);
+    assert.strictEqual(result.success, true, `render-checkpoint failed: ${result.error}`);
+    assert.ok(result.output.includes('This block has no trailing YAML key.'));
+    assert.ok(result.output.includes('It ends at the section boundary.'));
+  });
+
   test('fails when testing is already complete', () => {
     fs.writeFileSync(uatPath, `---
 status: complete