fix: Discord memory bug — add session continuity + 6 memory system fixes (#147)

Discord created a new agent per message with no conversation history,
causing Timmy to lose context between messages (the "yes" bug). Now uses
a singleton agent with per-channel/thread session_id, matching the
dashboard's session.py pattern. Also applies _clean_response() to strip
hallucinated tool-call JSON from Discord output.

Additional fixes:
- get_system_context() no longer clears the handoff file (was destroying
  session context on every agent creation)
- Orchestrator uses HotMemory.read() to auto-create MEMORY.md if missing
- vector_store DB_PATH anchored to __file__ instead of relative CWD
- brain/schema.py: removed invalid .load dot-commands from INIT_SQL
- tools_intro: fixed wrong table name 'vectors' → 'chunks' in tier3 check

Co-authored-by: Trip T <trip@local>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

tests/timmy/test_agents_timmy.py

@@ -63,8 +63,17 @@ class TestBuildContext:
         memory_file.write_text("# Important memories\nRemember this.")
         mock_settings.repo_root = str(tmp_path)
 
-        ctx = build_timmy_context_sync()
-        assert "Important memories" in ctx["memory"]
+        # Patch HotMemory path so it reads from tmp_path
+        from timmy.memory_system import memory_system
+        original_path = memory_system.hot.path
+        memory_system.hot.path = memory_file
+        memory_system.hot._content = None  # Clear cache
+        try:
+            ctx = build_timmy_context_sync()
+            assert "Important memories" in ctx["memory"]
+        finally:
+            memory_system.hot.path = original_path
+            memory_system.hot._content = None
 
 
 class TestFormatPrompt: