Scope pr-gate-city mayor to city so W3 step 7 yields one mayor

Without an agent.toml the pack's mayor had no scope, so gascity projected
it at city scope AND into every rig. W3 step 7's check
(gc config show | grep -A1 '^\[\[agent\]\]' | grep -c '^name = "mayor"')
returned 3 instead of 1.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: austinborn

artifacts/packs/pr-gate-city/agents/mayor/agent.toml

@@ -0,0 +1,9 @@
+# Mayor — city-scoped persona that carries the PR gate.
+#
+# `scope = "city"` is load-bearing. A pack agent with no scope is projected
+# at BOTH city scope and into every rig, so without this file the pack's
+# mayor lands twice (once as `mayor`, once as `ascii-art/mayor`) on top of
+# the city's own agents/mayor/ — three mayors where W3 expects one.
+
+scope = "city"
+prompt_template = "agents/mayor/prompt.template.md"