feat(design): every button on its family, the chip primitive, the lint rule (E28 S3b2)

The second half of the button sweep: the remaining hand-rolled buttons in
feature components, the design lab and the components/ui composites now
stand on Button, IconButton, Pressable, Chip or DragHandle.

- Chip + DismissibleChip (filter / token / tag / suggest / ghost, 24px
  floor, 44 on touch) replace five chip geometries; FilterChipGroup
  renders Chips; overflow lanes measure a mirror painted by chipClass.
- The Plex control row is IconButton's player rung (36, 20px glyph,
  round, overlay; 44 on touch); the YT modal bar is on the sm rung with
  pressed cycle toggles and names that survive a folded label.
- New variants: IconButton ghost-accent, danger-soft; Button warn on a
  new state-warn utility. The .btn-{tone} recipes and btnCls are gone.
- Fixed on the way: membership rows (collection editor, Plex playlist
  add) announce checked/mixed; a one-letter tag chip was 21px wide;
  descriptionLinks moved out of lib/ (it renders components).
- local/button-primitive: a raw <button>/<FocusSafeButton> outside the
  control-primitive files is a lint error (contract-tested, seen red).

frontend/src/components/ui/README.md

@@ -39,7 +39,7 @@ domain-free.
 | area                   | components                                                                                                                                                                                                                                                                                                                                                                                                           |
 | ---------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | overlays & anchoring   | `AnchoredPopover` + `anchoredPopoverHooks` (the popover engine: arrows, typeahead, Escape, anchor-flip), `ActionMenu`, `ContextMenu` + `useContextMenu` (the SAME menu, opened by right-click / long-press / Shift+F10), `Modal`, `Overlay`, `SidePanel`, `Tooltip`, `Toaster` (+ `toastLevels`, `overlayOrder`; `lib/toastDock` docks one control under the stack, in every host), `CommandPalette`, `KeyboardHelp` |
-| actions & inputs       | `Button`, `IconButton`, `Pressable`, `DragHandle` (one per button family, docs/DESIGN.md), `form`, `DraftSaveBar`, `Combobox`, `FilterSelect`, `SegmentedToggle`, `SortControl`, `ColumnSortControl`, `PriorityStepper`, `UndoToolbar`                                                                                                                                                                               |
+| actions & inputs       | `Button`, `IconButton`, `Pressable`, `Chip` + `chipStyles`, `DragHandle` (one per button family, docs/DESIGN.md; a raw `<button>` outside this folder is a lint error), `form`, `DraftSaveBar`, `Combobox`, `FilterSelect`, `SegmentedToggle`, `SortControl`, `ColumnSortControl`, `PriorityStepper`, `UndoToolbar`                                                                                                  |
 | data display           | `DataTable`, `tableHeader` + `tableAlign`, `Pager` + `pagerContent`, `VirtualGrid` + `gridColumns` (the column/width maths, incl. the ultrawide `maxCols` cap), `readAhead`, `Carousel`, `NavGrid` (a plain grid, list or table body the keyboard walks — `DataTable`, `VirtualGrid` and `Carousel` take `keyboardNav`), `Avatar`, `CountBadge`, `ItemCount`, `FilterChipGroup`                                      |
 | page & panel structure | `PageShell` + `pageToolbarSlot`, `PageScroller`, `PanelGroup`, `PanelGroups`, `Tabs`, `BackToTop`                                                                                                                                                                                                                                                                                                                    |
 | state & messaging      | `QueryState`, `Banner`, `InlineNotice`                                                                                                                                                                                                                                                                                                                                                                               |
@@ -51,9 +51,9 @@ are not a target — see [`docs/DESIGN.md`](../../../../docs/DESIGN.md) § Devic
 change at 1024x768, 820x1180 and a desktop size. That contract lives in these components, not in the
 ~160 call sites, because a rule repeated in 160 places is a rule that is already broken somewhere:
 
-- **Geometry is a ladder, not a free choice.** `Button`'s `SIZES` and `IconButton`'s sizes are the
-  rungs docs/DESIGN.md decided (B1: 24 / 28 / 32, icons 28 / 32). Pick a rung; do not hand-roll
-  padding on a primitive.
+- **Geometry is a ladder, not a free choice.** `Button`'s `SIZES`, `IconButton`'s and `Chip`'s sizes
+  are the rungs docs/DESIGN.md decided (B1: 24 / 28 / 32, icons 28 / 32, chips 24 / 28; the C5 media
+  and player rungs). Pick a rung; do not hand-roll padding on a primitive.
 - **Type, padding and box geometry are rem-derived**, so the Settings text-size slider (`--font-scale`
   on the root font-size) scales boxes and padding with the label. A `text-[Npx]` font size is an
   eslint error for exactly this reason. The deliberate exceptions are the layout-engine measurements