Fix the unreachable unknown-database-type guard (#1091)

[gangster]

Fixes #1091.

!name in config parses as (!name) in config, so the guard tested whether the boolean false was a key of the config object. It never is, so the throw was unreachable for every input, and an unrecognised --db value failed two lines later instead:

$ npm test --db=postgres
TypeError: config[name] is not a function
npm error code 7

-  if (!name in config) {
+  if (!Object.hasOwn(config, name)) {
     throw new Error(`unknown database type '${dbType}'`)
   }

Why Object.hasOwn rather than !(name in config)

The minimal correction fixes the precedence but leaves a second hole, because in walks the prototype chain and config is a plain object literal. On current main:

$ npm_config_db=toString node -e "require('./app/config.js')"
no error. db config = {"type":"toString","connect":"[object Object]","debug":false}

config.toString(parts) returns the string "[object Object]", which is passed on as the connection settings and fails somewhere less obvious in db.js. !(name in config) would not catch that; hasOwn does, at the same length. Same bug class as #1089.

Verification

Unknown types now produce the intended message:

--db=postgres      Error: unknown database type 'postgres'
--db=toString      Error: unknown database type 'toString'
--db=constructor   Error: unknown database type 'constructor'
--db=banana        Error: unknown database type 'banana'

Valid types are unchanged:

--db=	resolves to
sqlite	type=sqlite connect={"name":":memory:"}
mysql	type=mysql connect={"host":"db","port":3306,...}
sqlite:../bin/events.db	type=sqlite connect={"name":".../bin/events.db"}
(none)	type=mysql

The sqlite:<path> row is the one worth noting: the guard sits immediately after dbType.split(':'), so it confirms the parts handling still works.

npm test is 53/53, and npm test --db=sqlite also passes.

No test

config.js reads the environment at require time and exports a plain object, so there is no seam to assert against without exporting getDatabaseConfig for testing. That is the house pattern elsewhere (calEventValidator, ical.js), but it widens the module's surface for a one-line fix, so I left it alone and verified manually as above. Happy to add it if you would rather have the coverage.

Object.hasOwn needs Node 16.9+; docker-compose.yml pins node:24.15.0-slim.