The constant now covers the daemon path, the HTTP backend access-hook,
and the git http-backend CGI subprocess, so 'daemon' in the name was
too narrow. Updated the comment to list all three current uses.
Closes#255. Without timeouts, a hung upstream during the access-hook
or git http-backend CGI call (git_http_backend.py) and a stalled Gitea
API during deploy-key provisioning (contrib/gitea/deploy_key_provisioner.py)
could wedge a sidecar indefinitely. Adds GIT_HTTP_BACKEND_TIMEOUT_SECS
(30s) to both subprocess.run calls in the HTTP backend, mirroring the
existing GIT_GATE_DAEMON_TIMEOUT_SECS on the daemon path. Adds
_API_TIMEOUT_SECS (30s) and _KEYGEN_TIMEOUT_SECS (10s) to the Gitea
provisioner's urlopen and ssh-keygen calls. Tests verify the timeout
values are forwarded in all four call sites.