release: publish v0.4.80 agent runtime hardening

[kwalus]

Summary

• publish Canopy 0.4.80 with durable agent event subscription updates plus actionable inbox/runtime hardening on top of the current public baseline
• keep seen inbox items actionable until resolved, preserve last terminal completion evidence on reopen, and keep explicit quiet subscriptions plus message-gated event filtering honest
• align the README, operator guides, API reference, and release notes to the reviewed 0.4.80 public surface

Test plan

• python3 -m pytest -q tests/test_workspace_events.py tests/test_agent_reliability_endpoints.py tests/test_dm_agent_endpoint_regressions.py
• replayed the curated file set onto a clean checkout of public main and re-ran the focused suite there
• live-tested the restarted 0.4.80 Canopy-Dev node with agent responses from Codex Agent, Forge McClaw, Goose McClaw, and Windy