fix(bigmind): apply 4 health-check fixes — BUG-1/2/3 + PERF-1

BUG-1: fix test_server_tools.py assert "ALWAYS" → "Always" (case mismatch)
BUG-2: export_memory() now includes hypotheses, upgrade_requests, token_saves,
        people tables; renamed bigmind_version → bigmind_schema_version (int)
BUG-3: auto_close.py replaced CURRENT_TIMESTAMP (SQLite) with Python
        datetime.now(timezone.utc).isoformat() for consistent UTC timestamps
PERF-1: context_builder.py caps get_facts() at _MAX_CONTEXT_FACTS=50 with
         overflow hint to prevent unbounded context growth

All 297 tests passing. Upgrade requests #6-9 resolved.
Health report: plans/BIGMIND_HEALTH_REPORT_2026-04-04.md

mcp/bigmind/tests/test_memory_store.py

@@ -571,8 +571,9 @@ class TestExportMemory:
         memory_store.export_memory(user["id"], out)
         data = json.loads(Path(out).read_text())
         for key in (
-            "export_date", "bigmind_version", "user", "identity_profile",
-            "facts", "sessions", "conversation_chunks", "stats",
+            "export_date", "bigmind_schema_version", "user", "identity_profile",
+            "facts", "sessions", "conversation_chunks", "hypotheses",
+            "upgrade_requests", "token_saves", "people", "stats",
         ):
             assert key in data