docs: the full system rollout runbook and the miner announcement

[BANADDA]

Step 12 of the full system plan.

docs/full_system_rollout.md:

• what is already on main, by PR;
• the order before the first system arena opens: boundary merges and fleet update, server and gateway deploys, choosing the arena, arena dials (escalation allowlist and prices, reference cost in micro USD, floor, target line), escalation mirrors, corpus, validator gateway settings, the intake archiver, then the announcement and the usual open;
• the dials to confirm, with their current values;
• a draft announcement for miners, to send one round ahead.

Docs only.

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