Remove Trino: Superset reads fuel-db directly as fuel_ro (PD-14)

trino/ deleted; the role trino_ro becomes fuel_ro, its password read from a
secret file at connect time; dashboards' SQL and column list for PostgreSQL;
the Compose project is renamed petrolyst, with volumes pinned to their old
names. AGENTS.md points to the architecture context. Not deployed: the next
deploy needs README's one-time steps first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

stacks/fuel-monitoring/fuel-db/migrations/0002_fm_derivations.sql

@@ -1,4 +1,4 @@
--- 0002_fm_derivations.sql: internal derivations in schema `fm` (not visible to Trino).
+-- 0002_fm_derivations.sql: internal derivations in schema `fm` (not readable by fuel_ro).
 -- DRAFT, not applied. Applied after 0001 by a loader acting as fuel_owner (README in this folder).
 -- Design: fuel-monitoring .context/plans/2026-10-24-fuel-db-baseline-dashboard.md, §4 and §5.1.
 BEGIN;