feat: Add update checker tooling

Add the initial dataset, version checker, tests, and project setup files so the update checker can be run and validated.

README.md

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+# check-for-updates
+
+Small Python script to compare running service versions against upstream releases.
+
+## Requirements
+
+- Python 3.10+
+
+## Setup
+
+Create and activate a virtual environment, then install dependencies:
+
+```bash
+python -m venv .venv
+source .venv/bin/activate
+pip install -e .[dev]
+```
+
+Copy `.env.sample` to `.env` and fill required values. Export the variables before running the script:
+
+```bash
+export PAPERLESS_API_TOKEN=...
+export RADICALE_BASIC_AUTH=...
+```
+
+## Usage
+
+```bash
+python3 check_updates.py --config services.yaml
+python3 check_updates.py --config services.yaml --all
+```
+
+## Tests
+
+```bash
+python -m pytest
+```