refactor(security): move all database access into pkg/security/lookup

pkg/security no longer contains SQL. Every provider calls a store interface
from lookup, implemented by a procedure backend (Postgres stored procedures,
the default there) and a direct backend (dialect-driven SQL for postgres,
sqlite, mysql and mssql with configurable table and column names).

- add sectypes, lookup, lookup/{dialect,procedure,direct,backends,ddl,conformance}
- split totp and providers sub packages out of the core package
- replace SQLNames/TableNames/QueryMode with lookup.Config (see breaking_changes.md)
- direct backend now covers column/row security and API-key login
- move txsettings SQL to lookup.ApplyTxSettings; remove password.go
- move schema scripts under lookup/, add reference DDL per dialect
- add a shared conformance suite; run it on sqlite, and on Postgres in a
  podman/docker container (RESOLVESPEC_TEST_CONTAINERS=1)
- fix procedure schema bugs found on real Postgres: duplicate p_data
  parameter, JSON null arrays, expires_at timezone casts, passkey list
  GROUP BY, missing resolvespec_passkey_login; accept zone-less timestamps

README.md

@@ -646,7 +646,7 @@ For documentation, see [pkg/cache/README.md](pkg/cache/README.md).
 
 #### Security
 
-Authentication and authorization framework with hooks integration. Database-backed providers use PostgreSQL stored procedures by default, with a portable Direct mode (plain Go/SQL) for SQLite, MySQL, or Postgres without the procedures installed.
+Authentication and authorization framework with hooks integration. Database-backed providers use PostgreSQL stored procedures by default, with a direct SQL backend (SQLite, MySQL, SQL Server, or Postgres without the procedures) selected through `lookup.Config`.
 
 For documentation, see [pkg/security/README.md](pkg/security/README.md) (see "Direct Mode" for the SQLite/portable-SQL path).