feat(agent-pod): persistent per-role agent pool, concurrency moves to repo level

coordinator.js now runs one long-lived planner/investigator/implementer/judge
session per repo (reused across every task via tmux send-keys) instead of a
fresh spawn per task per stage. Tasks within a repo run sequentially against
that pool; concurrency is now REPO_CONCURRENCY (default 3) concurrent repos
via a new --repos flag, not concurrent tasks in one repo's phase.

k8s/apps/agent-pod/deployment.yaml

@@ -31,15 +31,17 @@ spec:
         # Also builds the agent-manager fork (github.com/Riotpiaole/
         # agent-manager, add-headless-spawn branch) from source and drops
         # coordinator.js in beside hub.js -- neither is the container's
-        # foreground process. hub.js keeps that role unchanged; running
-        # multiple repos' pipelines concurrently in this one pod means
-        # `kubectl exec <pod> -- node /root/coordinator.js --repo X --tasks
-        # Y &` once per repo, each an independent process inside the same
-        # container, each spawning its own agent-manager-tracked sessions
-        # on the container's local tmux server -- `kubectl exec -it <pod>
-        # -- agent-manager` attaches its TUI live against those same
-        # sessions, no cross-machine visibility problem since spawner,
-        # tmux server, and viewer are all colocated here.
+        # foreground process. hub.js keeps that role unchanged; coordinator.js
+        # itself now owns multi-repo concurrency (REPO_CONCURRENCY env,
+        # default 3), so one invocation handles every repo:
+        # `kubectl exec <pod> -- node /root/coordinator.js --repos
+        # repoA,repoB,... --tasks ...`. Each repo gets its own clone and its
+        # own persistent 4-agent pool (planner/investigator/implementer/
+        # judge, one agent-manager session per role, reused across every
+        # task in that repo) on the container's local tmux server --
+        # `kubectl exec -it <pod> -- agent-manager` attaches its TUI live
+        # against those same sessions, no cross-machine visibility problem
+        # since spawner, tmux server, and viewer are all colocated here.
         #
         # No prebuilt Linux binary is shipped for agent-manager: the local
         # .bin/ build is macOS arm64 (wrong OS/arch for this container