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/yahoo-history.json.golden

@@ -0,0 +1,29 @@
+exit: 0
+--- stdout
+[
+  {
+    "date": "2024-03-01",
+    "open": 9800,
+    "high": 9900,
+    "low": 9750,
+    "close": 9875,
+    "volume": 12300000
+  },
+  {
+    "date": "2024-03-02",
+    "open": 9850,
+    "high": 9920,
+    "low": 9800,
+    "close": 9880,
+    "volume": 11000000
+  },
+  {
+    "date": "2024-03-03",
+    "open": 9860,
+    "high": 9950,
+    "low": 9820,
+    "close": 9925,
+    "volume": 14000000
+  }
+]
+--- stderr