Feat(search): Support query parameter to preconfigure Search page

[elainefan331]

Description:
Support a partner preset deeplink like ?dbname= that preconfigures the Search page, so partners can link users to:

https://neurojson.io/search?dbname=<valid-db-id>

Tasks:

• Implement reading preset database from the query string and apply the preset’s initial form state.
• Support a generic preset (?dbname=) that accepts any registry database id.

Acceptance Criteria:

• Visiting /search?dbname= initializes with that database selected.
• Visiting /search?dbname= leaves database as “any” and the app renders without errors or console warnings.