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>

src/brain/schema.py

@@ -7,9 +7,9 @@ SQL to initialize rqlite with memories and tasks tables.
 SCHEMA_VERSION = 1
 
 INIT_SQL = """
--- Enable SQLite extensions
-.load vector0
-.load vec0
+-- Note: sqlite-vec extensions must be loaded programmatically
+-- via conn.load_extension("vector0") / conn.load_extension("vec0")
+-- before executing this schema. Dot-commands are CLI-only.
 
 -- Memories table with vector search
 CREATE TABLE IF NOT EXISTS memories (