Plugin config text fields ignore the schema's required list and never seed defaults #357

convertToFormkit (src/dispatch/static/dispatch/src/plugin/store.js) sets validation: "required" on every type: string field unconditionally, and — unlike the integer branch — never copies value.default into the generated object.

So a field the server lists as optional renders as required-and-blank even when the schema supplies a default. Verified against the emitted schemas for all 22 registered plugins: 29 optional string properties are affected, including the whole slack-conversation.slack_command_* set (each with a non-null default such as /dispatch-list-tasks), aws-sqs-signal-consumer.region, pagerduty-oncall.pagerduty_api_url, and model/system_message on both AI plugins.

Impact is a misleading form rather than a hard block: the save button binds to the surrounding Vuetify v-form, not FormKit's validity, so the required rule surfaces a message without preventing submit.

The correct signal is the schema's top-level required array, which convertToFormkit currently never reads.

Out of scope for #294 (PR #356), which fixed only the anyOf type lift; #294 adds profile_department_field_id to the affected set.