feat: add table group field for organizing and filtering Huf Data Tables

[esafwan]

Summary

• Adds a simple, free-form table_group string field (label: "Group") to the Huf Data Table registry doctype — a user-chosen label, not a fixed enum or a separate management doctype (deliberately kept simple per the request: "group name it chooses").
• Where you manage it: the same "Table Settings" panel used both when creating a new table and when editing an existing one's schema — right alongside Table Name/Description. No separate "manage groups" screen exists (or is needed) — group names are just derived from whatever values exist across your tables.
• Autosuggest existing groups: the Group field suggests group names already in use (native <datalist>) with a small "Existing groups: ..." hint below it, so you can reuse a group instead of retyping it, while still being free to type a new one.
• Visual hierarchy pass: applied the same primary/secondary field pattern the Add Tool form uses (ToolCreationForm.tsx's "Additional Settings" section) to both the Table Settings panel and the Field Properties panel — not every field is equally important, so they shouldn't look equally prominent. Table Name/Description (and Label, for a field) stay full-size and up top; Group/Icon/Naming Method (and Default Value/Help Text/Properties, for a field) — things that default sensibly and are rarely touched — now sit under a smaller, muted "ADDITIONAL SETTINGS" heading with more compact inputs.
• The Data tables listing page groups table cards under section headers by their group value, with an "Ungrouped" bucket for tables that don't set one.
• Simple/Grouped view toggle: a toggle (list/layers icons) next to the search box switches between a flat card grid and the grouped view. Defaults to the flat/simple view automatically when the table count is small (≤ 3), regardless of whether any group is set, and only appears once at least one table has a group assigned.
• Fully backward compatible — existing tables with no group render under "Ungrouped" (or flat, if few tables) with no behavior change otherwise.
• This is intentionally just the grouping/labeling primitive — a future PR (mentioned by the user as "huf-app in a future PR") can build richer grouping/filtering UX on top of this field without a schema change.

Note for reviewers: this PR and #458 (builder-form-ux) both touch TableSettingsPanel.tsx/FieldConfigPanel.tsx independently (branched from the same base before either merged) — expect a rebase/merge-order conversation before both land.

Screenshots (live bench, before → after)

Before (flat list, all under implicit grouping):

After — grouped view (Customers set to group "Sales", Students remains "Ungrouped"):

Toggle — simple view (default when table count is small):

Toggle — grouped view (switched manually):

Group field autosuggest:

Visual hierarchy — Table Settings (primary fields up top, secondary under "ADDITIONAL SETTINGS"):

Visual hierarchy — Field Properties (Label primary, Default/Help Text/Properties demoted):

Test plan

• yarn typecheck — 0 errors
• yarn lint — 0 errors (60 pre-existing unrelated warnings)
• Verified live on bench at every step: grouping/filtering, the view toggle, group autosuggest, and the hierarchy restructure all confirmed visually on the running app, not just via diff review

[esafwan]

Superseded by consolidated Data Tables PR #460, now included in integration PR #468.