Refactor Hub tenant themes for SurveyJS 3 (paged API, Endatix client, vertical slice)

[PeterMarinov]

Goal

Make tenant Theme Editor logic easy to maintain through the SurveyJS 3 upgrade: consume paged GET /themes, talk to the API only via lib/endatix-api, and keep CRUD + Creator dialogs in a dedicated features/themes vertical slice—not nested under forms/.

Parent: endatix-hub#908 (SurveyJS 3.0.2). API envelope: endatix#991. Same Hub paging pattern as form templates (endatix#990).

Implementation Notes

Work is in the Hub branch that also lands SurveyJS 3. Track here so review and release notes stay on the themes refactor, not the whole upgrade.

Paged client (lib/endatix-api/themes/)

• list() returns one NormalizedPagedResponse page (items, hasNextPage, totals).
• listAll() drains pages for the Theme Editor chooser (no paging UI), bounded max pages.
• Query builder: paging + sort + created/modified filters (buildListThemesEndpoint).
• Path ids via validateEndatixId on update/delete.
• Drop getThemes / parseThemesPayload from services/api.ts. Paged envelope only—no array dual-read.

Server actions

• Map ApiResult with toResult(...). Chooser uses listAll.
• Keep action names (getThemesAction, createThemeAction, …) to limit churn.

Vertical slice (features/themes/)

Slice	Role
create-theme / update-theme / delete-theme / list-themes	CRUD actions
list-forms-for-theme	Delete guard
update-form-theme	Assign themeId on a form
manage-theme-editor	Hook + save/delete dialogs

• Shared: types.ts (StoredTheme). Client barrel index.ts (UI/hook only). Actions via server.ts or slice paths—do not re-export "use server" from the client barrel.
• Form editor still hosts Creator; import theme UI from @/features/themes/manage-theme-editor.
• Hub chrome / SurveyJS tokens stay in lib/themes/ (not tenant CRUD).

Docs

• hub/project-structure.md (Themes table), hub/DESIGN.md, hub/AGENTS.md, ARCHITECTURE.md (dialog paths).

Acceptance Criteria

• Hub reads GET /themes as Paged.items only (Theme Editor not empty against API after #991).
• Theme HTTP lives in lib/endatix-api/themes/ with list vs listAll; tests cover the query contract.
• Theme actions live under features/themes/{verb-noun}/ and return Result via toResult.
• Theme save/delete dialogs + useThemeManagement live in manage-theme-editor; form editor imports them.
• lib/themes/ remains Hub product tokens only.
• Unit tests for actions, dialogs, and the management hook pass.