feat(kanban): add configurable gateway notification profiles

[whirmill]

Summary

• Adds a configurable Kanban gateway notification profile so deployments can choose less noisy board updates without hardcoding local policy into the gateway.
• Adds balanced thread naming/formatting for Kanban notifications while preserving more verbose/audit-style behavior behind profile selection.
• Updates Kanban notify tests and board dispatch behavior around live spawn capacity.

Testing

• python -m pytest tests/gateway/test_kanban_notifier.py tests/hermes_cli/test_kanban_notify.py -o 'addopts=' -q
• Included in combined local convergence run: 272 passed

Notes

This is intentionally separate from the Discord handoff membership fix and the model/context fallback fixes so the upstream review can evaluate the Kanban UX policy independently.

[teknium1]

Thanks @whirmill — closing this one. 875 LOC of UX policy (notification profiles, thread naming, dispatch behavior tweaks) is substantive design territory. It also overlaps with #26348 (notification_sources, already merged) and the existing per-task notify-sub model. Worth doing if there's a concrete gap the existing surfaces don't fill, but the design conversation needs to come first. If you want to revisit as a fresh focused PR, happy to take another look.