feat: add conversation persistence and context management layer

- SQLAlchemy async database layer (SQLite dev, PostgreSQL prod)
- Conversation and Message models with UUID primary keys
- Token counting utilities using litellm
- Context summarization at 80% token threshold
- REST API endpoints for multi-turn conversations
- 19 conversation tests, 6 token tests (176 total passing)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,31 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.4.0] - 2026-01-11
+
+### Added
+- Conversation persistence layer with SQLAlchemy async
+  - Database models: `Conversation`, `Message` with UUID primary keys
+  - SQLite (dev) and PostgreSQL (prod) support via async engines
+  - Lazy database initialization pattern
+- Context management infrastructure
+  - Token counting utilities using `litellm`
+  - Context summarization at 80% token threshold
+  - XML-tagged context prompt building for agent injection
+- REST API for multi-turn conversations
+  - `POST /conversations/` - Create new conversation
+  - `GET /conversations/` - List conversations
+  - `GET /conversations/{id}` - Get conversation with history
+  - `POST /conversations/{id}/messages` - Add message (triggers agent)
+  - `DELETE /conversations/{id}` - Delete conversation
+- New dependencies: `sqlalchemy[asyncio]~=2.0.36`, `aiosqlite~=0.21.0`, `litellm~=1.57.0`
+- Config settings: `database_url`, `summarization_threshold`, `keep_recent_messages`
+- 19 conversation tests, 6 token counting tests (176 total tests passing)
+
+### Changed
+- Updated COVERAGE.md to ~80% complete
+- Quieter pytest output (`-q --tb=short` instead of `-v`)
+
 ## [0.3.4] - 2026-01-11
 
 ### Added