fixtures: golden data dir — real records, production read paths

Owner-manufactured teach master (chat_mv27rrra: compaction, subagent-abort,
every teach tool) + practice lifecycle (chat_mv293wv5: the full marker cycle
including the first-ever problem-dismissed), the real graph ledgers, five
jobs across the kind x status matrix, and settings. tests/golden-fixtures
reads all of it through the stores via the LH_DATA_DIR seam and pins the
fixture law: real data parses, flattens to a legal LLM wire, derives the
graph, covers every custom-marker kind, and reads never write.

Fixture law: an intentional format change updates these files in the same
commit; an unintentional one fails the suite.

tests/fixtures/golden-data/jobs/job_mux5xn7v_b49f3458.json

@@ -0,0 +1,14 @@
+{
+	"id": "job_mux5xn7v_b49f3458",
+	"kind": "research",
+	"chatId": "chat_mux5xn73_b1ccd21e",
+	"toolCallId": "call-mid",
+	"status": "done",
+	"activity": "delivered",
+	"createdAt": "2026-10-06T21:00:31.819Z",
+	"updatedAt": "2026-10-06T21:00:32.122Z",
+	"result": {
+		"brief": "Mid-run brief.",
+		"sources": []
+	}
+}