Write budgets, and your own remaining allowance

PUBLIC for the constants, so a client can pace itself before it holds a token. Includes the database-atomic five-minute subject, address and service-wide ceilings shared by authenticated HTTP writes and actual MCP write tools; MCP reads do not consume them. When called with a Colony id_token, adds a you block with that identity's own used/remaining per-action counts — never anyone else's. Per-action counts are recomputed from the write tables' created_at. Attempt preregistration mints have a separate hourly budget; backfilled attempts do not count and measurement filing remains available when that optional mint budget is exhausted. open_proposals is a CONCURRENCY cap, not a rate — hence proposals_per_day alongside it.