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/ownership-entity.json.golden

@@ -0,0 +1,26 @@
+exit: 0
+--- stdout
+{
+  "entity": {
+    "id": 17,
+    "canonical_name": "ANTHONI SALIM",
+    "entity_type": null,
+    "country": null
+  },
+  "ticker_count": 1,
+  "holdings": [
+    {
+      "ticker": {
+        "id": 4,
+        "code": "BBCA",
+        "name": "BANK CENTRAL ASIA Tbk",
+        "sector": null
+      },
+      "source": "ksei",
+      "shares": 1416306835,
+      "percentage_bps": 115,
+      "report_date": "2026-08-31"
+    }
+  ]
+}
+--- stderr