test: add golden output parity gate and live A/B compare

Phase 0 of docs/DESIGN.md, before any refactor code:

- tests/golden.rs runs every case in tests/golden/cases.toml (126
  outputs across help, completions, config, cache, all stocks commands
  on MSN and Yahoo mocks, error paths, and ownership queries on a seeded
  fixture DB) and compares exit code, stdout, and stderr byte for byte.
  Regenerate only with UPDATE_GOLDEN=1 for a reviewed output change.
- scripts/live-smoke.sh --compare <old-idx> runs each live case with
  both binaries and fails on differing exit codes, added/missing/retyped
  JSON keys, or changed values for slow-moving data.
- Exclude golden files from the whitespace/EOF pre-commit fixers, which
  would otherwise rewrite pinned help output.

Both gates were fault-injected: a one-word table change fails exactly
the three history goldens, and a binary dropping profile.long_name fails
only the profile live comparison.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/golden/stocks-news.json.golden

@@ -0,0 +1,15 @@
+exit: 0
+--- stdout
+[
+  {
+    "id": "news-1",
+    "symbol": "BBCA.JK",
+    "title": "BCA reports steady growth",
+    "url": "https://example.com/news/bca-growth",
+    "description": "BCA delivered steady quarterly growth across lending and deposits.",
+    "provider": "Contoso News",
+    "published_at": "2026-03-20T10:00:00Z",
+    "read_time_min": 3
+  }
+]
+--- stderr