Self-hosting slice 1b, lane B: sybil-proof credit, pay-for-work epoch statements, live Postgres #1770

Part of #1761, lane B ("honest economics"). See #1756.

Lane B's three rows of #1761, on top of slice 1 (#1760) on the integration branch hosting-mvp:

1. Sybil-proof credit. The runtime for gHashTag/t27 specs/hosting/sybil.t27 (t27#8743): anchored quorum, canaries, probation, a per-key cap per epoch, attestation and the slash. It sits behind TRIOS_HOSTING_SYBIL=on.
2. Pay-for-work credits and epoch statements. The runtime for specs/hosting/statement.t27 (t27#8744, t27#8759):
   • every credit is named by kind (EXECUTOR_FEE, VERIFIER_FEE, slash);
   • each epoch closes into a statement signed with the Queen's ledger key;
   • GET /hosting/ledger/epochs and GET /hosting/ledger/epochs/:n/proof?key= serve them;
   • trios-host statement checks a host's own inclusion;
   • settlement stays shut and nothing moves value.
3. Live Postgres.
   • The hosting store runs against a real PostgreSQL 16 (tests/pglive/hosting-store-live.test.ts; it skips without TRIOS_PG_TEST_URL).
   • The boot migration is idempotent, and it builds nothing with TRIOS_HOSTING off.
   • The release follow-up: the ledger key comes from one variable, TRIOS_HOSTING_LEDGER_KEY. Without it, epochs stay open and unsigned.

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