Add fail-closed author allowlist gating job dispatch

Sessions run claude with --dangerously-skip-permissions and a prompt built
from issue/PR/comment text, so only trusted authors may supply that text.
teabot now dispatches a job only when the triggering event's author login is
on an allowlist; an empty allowlist dispatches nothing (fail-closed).

Claude-Session: https://claude.ai/code/session_015ur3i7D2azsMAWTSVABApv

config.example.yaml

@@ -36,6 +36,23 @@ claude_config_dir: ~/.claude
 # Optional: override the state directory (default ~/.local/state/teabot).
 # state_dir: ~/.local/state/teabot
 
+# SECURITY: author allowlist. Jobs run with --dangerously-skip-permissions in a
+# container whose prompt is built from issue/PR/comment TEXT, so only trusted
+# authors may supply that text. teabot dispatches a job only when the event's
+# author login is listed here. Events from anyone else are recorded (so they do
+# not re-trigger) and logged, but never spawn a container. This is fail-closed:
+# an empty/absent list dispatches NOTHING.
+allowed_authors:
+  - benvin
+
+# Optional per-repo override. A present entry fully replaces allowed_authors for
+# that repo (an empty list disables dispatch for it); absent falls back to the
+# global list above.
+# repo_allowed_authors:
+#   unkin/teabot:
+#     - benvin
+#     - trusted-colleague
+
 # Bot personalities. Each is a distinct Gitea account backed by its own tea
 # config file (create it with: tea logins add --name <bot> ...). teabot reads
 # the token + username from that file and mounts it into the container so tea