Improve en/api/ nav structure (root construct, hidden flags)

[digitaldiina]

Follow-up to #182 (Prune superseded/orphaned API reference pages) — once pruning decisions land, tune the remaining en/api/ nav the same way Contribute/Integrations were: adopt Mintlify's root construct for group index pages (currently only 2 uses of root in all of config/nav-en.json, both under the database/tables and automation/crmscript/reference trees — none in the API tab's own guide groups), and apply the hidden: true treatment to the NetServer-Core subfolders originally flagged in #109 (entities/rows/osql/sql/custom-objects/foreign-keys/caching/bulk-operations/lists/security/sentry/plugins/{sentry,document}) if not already applied — verify current state at implementation time, since some of this may have landed via #110/#124.

Blocked by: #182 (Prune superseded/orphaned API reference pages).

Verification: tools/verify-nav-paths.py, mint validate clean of new warnings.

[digitaldiina]

While doing nav/link work on the Guides tab (#179), found 4 REST reference links that don't resolve to any real file — surfacing them here since they'll likely be affected by the #182 pruning pass:

• en/admin/license/dev/index.mdx → /en/api/reference/restful/agent/License_Agent/v1LicenseAgent_GetUserLicenses
• en/admin/license/dev/index.mdx → /en/api/reference/restful/agent/License_Agent/v1License_GetThirdPartyLicenseAssignments
• en/admin/license/dev/index.mdx → /en/api/reference/restful/agent/License_Agent/v1User_GetCurrentPrincipal
• en/project/dev/index.mdx → /en/api/reference/restful/rest/project/index

Left these links as-is rather than guessing a replacement, since the correct target depends on whichever reference-generator naming these should map to (or whether they've simply been pruned already and the referring pages need updating). Flagging for whoever picks up #182/#183.