feat: Phase 2 Memory Core — structured memory with context integration

Memory Core implementation:
- Memory service with 6 types: identity, preference, project, episodic, knowledge, adaptation
- CRUD operations: create (with dedup), get (filtered), update, invalidate, supersede
- Confidence scoring (0.0-1.0) and lifecycle management (active/superseded/invalid)
- Memory API endpoints: POST/GET/PUT/DELETE /memory

Context builder integration (trust precedence per Master Plan):
  1. Trusted Project State (highest trust, 20% budget)
  2. Identity + Preference memories (10% budget)
  3. Retrieved chunks (remaining budget)

Also fixed database.py to use dynamic settings reference for test isolation.
45/45 tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/conftest.py

@@ -6,8 +6,9 @@ from pathlib import Path
 
 import pytest
 
-# Force test data directory
-os.environ["ATOCORE_DATA_DIR"] = tempfile.mkdtemp(prefix="atocore_test_")
+# Default test data directory — overridden per-test by fixtures
+_default_test_dir = tempfile.mkdtemp(prefix="atocore_test_")
+os.environ["ATOCORE_DATA_DIR"] = _default_test_dir
 os.environ["ATOCORE_DEBUG"] = "true"