Refactor forwarding API

[p-j-smith]

Follows-on from #43 to:

• make src/api a uv package in packages/api
• update the forwarding API Dockerfile to cache dependencies
• use DATA_FOLDER for mounting the forwarding API data volume
• update docs on installing pyonb and send docs to the forwarding API for processing
• tested locally, and test_inference_single_file_upload_kreuzberg and test_inference_on_folder_kreuzberg both pass (these tests use the forwarding API)

[Copilot]

Pull Request Overview

This PR refactors the forwarding API by converting it from a standalone module in src/api to a proper uv workspace package in packages/api. The main purpose is to improve the project structure and package management for the OCR forwarding API component.

• Moved the forwarding API from src/api to packages/api as a proper uv package
• Updated Docker configuration to use caching and better build practices
• Removed unused test functions and utility code that are no longer needed

Reviewed Changes

Copilot reviewed 10 out of 17 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/api/test_app.py	Removed unused imports and data folder validation test function
src/api/requirements.txt	Deleted old requirements file (moved to package configuration)
src/api/app/util.py	Removed utility functions that are no longer needed
src/api/Dockerfile	Deleted old Dockerfile (replaced with new one in packages/api)
pyproject.toml	Added API package to workspace and optional dependencies
packages/api/pyproject.toml	New package configuration with proper dependencies
packages/api/README.md	Added documentation for the forwarding API usage
packages/api/Dockerfile	New optimized Dockerfile with UV and dependency caching
docker-compose.yml	Updated build context and removed unnecessary volume mount
docker-compose-postgres.yml	Removed entire PostgreSQL configuration file

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