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

pkg/security/OAUTH2.md

@@ -21,7 +21,7 @@ The security package provides OAuth2 authentication support for any OAuth2-compl
 ### 1. Database Setup
 
 ```sql
--- Run the schema from database_schema.sql
+-- Run the schema from lookup/database_schema.sql
 CREATE TABLE IF NOT EXISTS users (
     id SERIAL PRIMARY KEY,
     username VARCHAR(255) NOT NULL UNIQUE,
@@ -53,7 +53,7 @@ CREATE TABLE IF NOT EXISTS user_sessions (
 );
 
 -- OAuth2 stored procedures (7 functions)
--- See database_schema.sql for full implementation
+-- See lookup/database_schema.sql for full implementation
 ```
 
 ### 2. Google OAuth2