fix: replace litellm with tiktoken for token counting

- litellm had dependency conflicts with pydantic-ai
- tiktoken is lighter and already required by pydantic-ai
- Updated documentation (README.md, architecture.md)

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

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.4.1] - 2026-01-11
+
+### Fixed
+- Replace `litellm` with `tiktoken` for token counting (dependency conflict with pydantic-ai)
+- Update documentation (README.md, architecture.md) with conversation layer info
+
 ## [0.4.0] - 2026-01-11
 
 ### Added
@@ -15,7 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - SQLite (dev) and PostgreSQL (prod) support via async engines
   - Lazy database initialization pattern
 - Context management infrastructure
-  - Token counting utilities using `litellm`
+  - Token counting utilities using `tiktoken`
   - Context summarization at 80% token threshold
   - XML-tagged context prompt building for agent injection
 - REST API for multi-turn conversations
@@ -24,7 +30,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - `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`
+- New dependencies: `sqlalchemy[asyncio]~=2.0.36`, `aiosqlite~=0.21.0`, `tiktoken>=0.12.0`
 - Config settings: `database_url`, `summarization_threshold`, `keep_recent_messages`
 - 19 conversation tests, 6 token counting tests (176 total tests passing)