Design module: component palette, drag and drop, emitted source

[pathscale]

Implements H6. A Design tab where you compose @pathscale/ui components on
an artboard and read the source they emit, live.

The two decisions H6 said to ask about

What is emitted: one IR, both emitters. document.ts is a tree edited by
pure functions that knows nothing about a target. emit/tsx.ts produces a
plain Solid component importing from @pathscale/ui, pasteable as-is.
emit/layout.ts produces the .layout.tsx and .recipe.ts pair
solid-layouts-library compiles, matching what chuzz already runs in
apps/chuzz/frontend/local-ui. Both are on screen behind a toggle. A third
target is a file and a line.

The two differ structurally, and the difference is not cosmetic: a layout
template has exactly one root element because slot.root has to land
somewhere, so it always wraps, while the TSX emitter returns a lone dropped
Button bare.

Where artboards render: the same document. Hit testing is
event.target.closest("[data-design-id]"), so no bridge is involved, the
control socket sees every node, and ps-qa can address each one by id. The
canvas takes pointer events in the capture phase and stops them there, which
is what lets a click select a real Button instead of pressing it, with no
pointer-events: none layer that would have broken the hit test it was
meant to serve.

The metadata gap

dist/layouts.manifest.json gives a name and a kind per component and
nothing a properties panel can read, so catalog.ts curates 22 entries by
hand: 7 layout, 9 display, 6 form. It is shaped like the recipe metadata the
library already carries, and each entry records the recipe it was
transcribed from, so a generator can replace it wholesale. Two notes for
whoever writes that generator, both learned here:

• Two recipe dialects exist upstream. Newer components call
  recipe({ props, defaults }); older ones export a CLASSES const whose
  nested keys are the same axes. It has to read both.
• The manifest is not an import list. Kbd is in it and is not exported
  from the package root. A curated entry for it typechecked as metadata and
  failed to compile the moment the canvas tried to render it, so it was
  dropped. Generating from the manifest alone would emit imports that do not
  resolve; cross-check dist/index.d.ts.

Verification

Per docs/ui-verification.md, the emitted source is asserted as text, which
is the deliverable and needs no renderer: dragging a Button onto an empty
canvas emits exactly the import and the element, and that is a string
comparison.

• bun run typecheck clean
• bun run lint clean, including both contract gates
• bun run test:run: 426 passed, 44 files, 32 tests new
• bun run build succeeds

Everything drives by accessible name as well as by pointer, so the palette,
the property rows, the target switch and the emitted source are all
reachable from ps-qa. The .ron outcomes for the Design tab are not in this
PR; the ui-control gate does not require them, because every input primitive
rendered on the canvas is one AgencyZero already imports and already covers.

Files outside features/design/

The ownership table gives this package features/design/ only. Five edits
land elsewhere, each the same shape the Analytics tab already uses, and each
one line or one block: the TabKind union, its icon in TAB_ICON, the pane
Match, the openDesign action, and the strip button. Plus the two i18n
catalogues, appended to.

Not done

No layers tree, no multi-artboard, no persistence: the document lives for
the life of the tab. No prop metadata generator, which by H6's own reading
belongs in UI/ and solid-layouts and needs its owner's agreement.