Add AGENTS.md for agents picking up work in new sessions

- AGENTS.md: ground rules (legal access, evidence, fairness), invariants
  that are easy to break, commands, and notes on the owner's dev machine;
  CLAUDE.md imports it
- backend/tests/Dockerfile.debian: test image from Debian packages for
  networks where PyPI is unreachable, documented in testing.md
- roadmap: list what v2 has not been verified against yet

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/contributing/testing.md

@@ -16,6 +16,20 @@ UPDATE_GOLDEN=1 pytest tests/test_golden.py   # regenerate expected outputs (rev
 
 Parsers are pure, so none of these needs a database or network.
 
+### Without PyPI access
+
+`tests/Dockerfile.debian` installs the dependencies from Debian packages instead (everything except
+`procrastinate` and `mcp`, which the tests don't need):
+
+```bash
+docker build -t politrack-test -f backend/tests/Dockerfile.debian backend/tests
+docker run --rm -v "$PWD/backend:/app" politrack-test python3 -m pytest -q -p no:cacheprovider
+```
+
+The same image can run adapters against the compose database: add `--network politics-tracking_default`
+and `-e POLITRACK_DATABASE_URL=postgresql://politrack:<password>@db:5432/politrack`, then
+`python3 -m politrack.cli run <adapter> --max-requests 20`.
+
 ## Golden fixtures
 
 ```