feat(obs): add operator dashboard views

[typelicious]

What changed

• adds operator-action summary cards and an operator-action breakdown table to the no-build dashboard
• surfaces GET /api/operator-events in the dashboard fetch path
• updates README, architecture docs, and changelog for the operator dashboard view

Why

• gives operators a read-only view of update checks and apply attempts without leaving the dashboard
• keeps operator observability inside the existing no-build UI

How verified

• python3 -m compileall foundrygate tests
• PYTHONPATH=. ./.venv-check-313/bin/pytest -q tests/test_metrics_traces.py tests/test_updates.py tests/test_config.py
• ./.venv-check-313/bin/ruff check foundrygate/main.py tests/test_metrics_traces.py
• ./.venv-check-313/bin/ruff format --check foundrygate/main.py tests/test_metrics_traces.py
• /usr/bin/git diff --check