ops(TC-1164): flip quota authority to billing

[samgbafa]

Refs TC-1162 / TC-1164.

MERGE ORDER: merge only after the step-4 migration is verified (billing /api/quota/<space> storage_limit_bytes ≥ floors and node override_bytes null for both spaces), and before any further deploy-phala dispatch. Merging alone triggers no deploy; it only builds images.

Changes

• ops/quota-overrides.json: authority → billing; secrets floor 268721121 → 1073741824 (Sam set 1 GiB via /storage 2026-10-17T05:36:53Z; internal D1 is the source); applications floor stays 5368709120. Comments now describe billing-mode floors.
• scripts/ci/reconcile-quota.py: LIMITS secrets → 1073741824; the node-override success message is built from LIMITS, so it can't drift from them.
• scripts/ci/test-quota-authority.py: fixture LIMITS updated; new test test_shipped_billing_config_reconciles_against_exact_floors.
• docs/releasing.md: billing is now described as the current authority, with the floors and the ordering/revert rule (reverting to node-override needs a reviewed PR).

Test coverage

Tests that already covered the guards, using synthetic configs: test_billing_mode_uses_absolute_limit_and_accepts_cold_node_cache (billing passes with no PUT), test_billing_absent_inactive_or_insufficient_fails_without_mutation (comp one byte below the floor), test_stale_local_override_rejects_billing_mode, and test_active_comp_on_second_space_blocks_every_legacy_put (authority mismatch).
What the new test adds: it runs full main() against the checked-in ops/quota-overrides.json, not a synthetic copy. With comps exactly at 5368709120 / 1073741824 and node override_bytes=null, it passes with zero PUT/DELETE. With the secrets comp at 1073741823 (one byte under the new floor), it fails billing authority does not cover both reviewed quota floors. With the shipped values in a temp copy set to node-override and an active comp, it fails authority mismatch: flip to billing with no PUT.

Tests

• python3 scripts/ci/test-quota-authority.py: 22 tests OK
• python3 scripts/ci/test-deploy-recovery.py: 17 tests OK
• python3 scripts/ci/reconcile-quota.py --validate-only: "Reviewed quota authority and targets validated."

[samgbafa]

APPROVE: see TC-1162 (reviewed exact head 2789efc)

[samgbafa]

APPROVE: see TC-1162 (reviewed exact head 004d9be)