POST /r/<owner>/<name>/edit reads the current .pr-review.json via the
Gitea contents API (404 → start from {}), updates static_message and
model, then PUTs the file back as the bot identity. Static message is
stripped and capped at 400 chars; model is validated against
cost_model.PRICES (unknown → flash + redirect, no save). CSRF token is
the dashboard auth token (same value, simplest binding).
Helpers (_http) moved to urllib.request at module top so tests can patch
the entry point; the helper returns the Gitea status code so 404 (file
missing) cleanly omits sha on the create-PUT path.
6 tests under tests/pilot/test_dashboard_edit.py covering the happy
path, the 400-char cap, the unknown-model rejection, auth + CSRF gates,
and the file-missing creation path.