Fetcher config

Each homework lives in hw/<homework>/ and carries its own fetcher_config.json, describing which repositories to fetch, which paths to pull, and where the test fixtures live:

{
  "org_owner": "uoabot-testing",
  "gh_token": "...",
  "homework": "hw0",
  "paths": ["aliquot/src/aliquot.c"],
  "tests": {
    "repo": "",
    "paths": []
  }
}

Field	Description
org_owner	GitHub organization that owns the repositories
gh_token	GitHub personal access token with read access to that organization
homework	Homework name, used to find the hw/<homework>/ directory
paths	File patterns to copy from each student repository
tests.repo	Repository holding the test fixtures (empty to skip)
tests.paths	File patterns to copy from the tests repository