Add ledger management service and API integration

- Introduced `LedgerService` to handle ledger file operations, queries, and snapshots.
- Added API routes for journal entry retrieval, account balances, and custom queries using FastAPI.
- Updated project dependencies to include `ruff` for linting, along with its configuration.
- Integrated `lifespan` for managing the lifecycle of `LedgerService`.

.idea/misc.xml

@@ -4,4 +4,7 @@
     <option name="sdkName" value="uv (ledger)" />
   </component>
   <component name="ProjectRootManager" version="2" project-jdk-name="uv (ledger)" project-jdk-type="Python SDK" />
+  <component name="RuffConfiguration">
+    <option name="enabled" value="true" />
+  </component>
 </project>