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/src/server.py

@@ -771,6 +771,8 @@ def memory_export(output_path: str = None) -> str:
         f"| **Facts** | {result['facts_count']} |\n"
         f"| **Sessions** | {result['sessions_count']} |\n"
         f"| **Chunks (Tier 3)** | {result['chunks_count']} |\n"
+        f"| **Hypotheses** | {result['hypotheses_count']} |\n"
+        f"| **People** | {result['people_count']} |\n"
         f"| **File size** | {result['file_size_kb']} KB |"
     )