chore: smoke test fixes and code quality improvements (#88)

* fix: replace deprecated datetime.utcnow() and websockets.legacy APIs

- Replace datetime.utcnow() with datetime.now(UTC) in Orderbook model
- Use websockets.asyncio.client.connect instead of legacy websockets.connect
- Import ConnectionClosed from websockets.exceptions directly
- Update test mocks to patch the new import paths

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: resolve ruff lint errors in alembic migration

- Replace typing.Union with X | Y syntax (UP007)
- Import Sequence from collections.abc instead of typing (UP035)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: remove deprecated version key from docker-compose.yml

The top-level 'version' key is obsolete in modern Docker Compose
and produces a warning.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: fix README to match actual project structure and tooling

- Replace pip commands with uv equivalents
- Fix run command from 'python -m src.main' to 'python -m polymarket_insider_tracker'
- Update project structure tree to reflect actual src/polymarket_insider_tracker/ layout

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -1,5 +1,3 @@
-version: "3.8"
-
 services:
   postgres:
     image: postgres:15