json_type insert option is parsed but has no effect in 13.7.2.1

## Question

`doc/configuration.md` shows `json_type` in the `insert_options` examples (e.g. `"json_type": "text"`), but setting it appears to do nothing. Is it still a supported option, or is it dead config that should be wired up or removed/documented?

## Observed

db-sync 13.7.2.1 (git db8cdf6), preview and a local testnet. Recreated the database from scratch under each setting:

- `json_type: text` -> the `.json` columns are `jsonb`
- `json_type: jsonb` -> the `.json` columns are `jsonb`

The `text` and `jsonb` settings produce an identical schema. Columns checked:
`tx_metadata.json`, `script.json`, `off_chain_pool_data.json`, `off_chain_vote_data.json` (all stay `jsonb`, which is also the default).

## Source

`sioJsonType` / `JsonTypeConfig` is defined and parsed in `cardano-db-sync/src/Cardano/DbSync/Config/Types.hs` (accepted values `text`, `jsonb`, `disable`; default `JsonTypeText`).

Grepping the tree, the only references to `JsonType` / `sioJsonType` are in that file plus the config-parse tests and a generator - there is no reference in any Schema, Migration, Insert or Query module.

So the value is validated and round-tripped in the config but never consumed, which matches the "no effect" behaviour above.

## Resolution

Either:

1. Wire `json_type` into the schema so `text` / `jsonb` / `disable` actually control the storage type of the JSON columns, or
2. If it is intentionally inert (superseded by `remove_jsonb_from_schema`), document that and/or remove it from the config and the examples so users do not set an option that does nothing.

Start with doc/configuration.md and JsonTypeConfig in cardano-db-sync/src/Cardano/DbSync/Config/Types.hs, then read the config-parse tests and generator references. Trace whether schema, migration, insert, or query modules consume the option; done means either wiring text/jsonb/disable into JSON column storage or removing the inert setting and documenting the replacement.

Written by the indexing model from the issue text.