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-insights.json.golden

@@ -0,0 +1,16 @@
+exit: 0
+--- stdout
+{
+  "id": "bn91jc",
+  "symbol": "BBCA.JK",
+  "summary": "Mixed analyst signals for Bank Central Asia Tbk PT: 1 positive, 1 negative, 1 neutral.",
+  "highlights": [
+    "P/E ratio: Earnings data unavailable, can't compare P/E ratio with peers",
+    "Analyst price target: Analysts forecast more than 20% upside for 12-month price target"
+  ],
+  "risks": [
+    "Quarterly Revenue YoY Growth: Revenue grew worse than peers"
+  ],
+  "last_updated": "2026-03-26T04:14:57.9197955Z"
+}
+--- stderr