[store] SqliteEpisodicStore — persistent episodic memory backend

[dgenio]

Context

Split from #41. Implements the SQLite-backed episodic memory store.

Depends on #40 (EpisodicStore protocol).

Acceptance Criteria

• SqliteEpisodicStore class in src/contextweaver/store/sqlite_episodic.py implementing EpisodicStore protocol
• Supports all EpisodicStore methods: save(), recall(), latest(), delete()
• Uses sqlite3 (stdlib) with WAL mode
• Supports :memory: mode for testing
• Deterministic ordering
• Passes the same test suite as InMemoryEpisodicStore via parameterized fixture
• Exported from src/contextweaver/store/__init__.py
• Full type hints, docstrings, from __future__ import annotations
• Module ≤300 lines

File Paths

• src/contextweaver/store/sqlite_episodic.py (new)
• src/contextweaver/store/__init__.py (edit — export)
• tests/test_store_episodic.py (edit — parameterize fixture)

Verification

make ci
pytest tests/test_store_episodic.py

Parent Issue

Part of #41 (SQLite-backed persistent stores).

[dgenio]

Consolidated into tracking epic #174. This issue's scope is now tracked as a checklist item there. Closing to reduce backlog noise — reopen if you need the detailed requirements.