feat(ui): Swatches panel header like InDesign's; swatches go to the fill or stroke in front

LYH Studio episode 6 colours the "1969" headline (8:28) and the loop's
stroke (9:15) from the Swatches panel, whose header holds InDesign's
Fill/Stroke proxy, Formatting Affects Container/Text and the Tint field.

- Header: a Fill/Stroke proxy showing the colours of what colour edits
  apply to (panels::color_target; a click brings the other to the front,
  as X does), the container/text buttons (app.formattingAffectsText) and
  the tint of the colour in front.
- The Tint field sends only the tint, so each selected object (or run of
  text) keeps its own swatch: object.fill takes a tint without a swatch,
  and a stroke tint alone doesn't give a stroke-less object a stroke.
- Clicking a swatch applies it to the fill or stroke in front
  (panels::apply_swatch, to the text when colours affect text); that row
  is highlighted.
- Bottom row: New Color Group, New Swatch, Delete Swatch (the swatch last
  clicked). Rows and the proxy are named for accessibility (and tests).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/target-app-parity.md

@@ -268,7 +268,7 @@ It is evidence of breadth: each item exists. It is not a claim of InDesign-level
 - Text engine: Knuth–Plass paragraph composer and single-line composer, dictionary hyphenation (public-domain Moby list + our own trained Liang patterns), justification with word/letter/glyph-scaling ranges, keep options (keep with next, keep lines together — at start/end of paragraph by default, as in InDesign — widows/orphans), balance ragged lines, optical margin alignment, hyphenation zone/limit, columns, threading across frames and spreads, tabs, bullets/numbering, rules, shading, baseline grid, first-baseline options, vertical justification, wrap exclusions, overset detection, caret/hit testing.
 - FID2: IDML underline/strikethrough Text Color resets survive style inheritance and roundtrip. Raster and PDF paint underlines behind glyphs, retain strikethrough above, and center rules on their offsets; synthetic overlap tests cover both backends.
 - Rendering: vello_cpu (SIMD, multithreaded) — pages, items, images with mip levels, gradients, composed text.
-- UI (egui): application bar + menus, Control panel (object and text modes), Tools panel with flyouts and the Fill/Stroke proxy (D, X, Shift+X, / as `color.*` commands), document tabs, rulers, pasteboard, guides (margins, columns, bleed, baseline grid), frame edges, selection handles, text ports and threads, Properties / Pages / Layers dock, Swatches, Styles, Character, Paragraph, Stroke, Text Wrap panels, New Document and Preferences dialogs, Quick Apply (⌘Return), 4 brightness themes.
+- UI (egui): application bar + menus, Control panel (object and text modes), Tools panel with flyouts and the Fill/Stroke proxy (D, X, Shift+X, / as `color.*` commands), document tabs, rulers, pasteboard, guides (margins, columns, bleed, baseline grid), frame edges, selection handles, text ports and threads, Properties / Pages / Layers dock, Swatches (InDesign's header: Fill/Stroke proxy, Formatting Affects Container/Text, Tint; a swatch goes to the fill or stroke in front; New Color Group / New Swatch / Delete Swatch row), Styles, Character, Paragraph, Stroke, Text Wrap panels, New Document and Preferences dialogs, Quick Apply (⌘Return), 4 brightness themes.
 - Pen tool, Direct Selection anchor/handle editing, rotate from corners, Rotate/Scale/Shear tools, Eyedropper, snapping & smart guides, Align/Distribute, Find/Change (text + GREP), Story Editor, Paragraph Style Options, Effects panel, hidden characters, native macOS menu bar, measured InDesign 2026 look (Medium Dark): Properties sections per selection state, 21 pt spinner fields with arithmetic, Contextual Task Bar, inverse (black) text selection, Pages panel with drag-and-drop reorder / parent apply, Layers panel with per-object rows.
 - Tools: Selection (click, marquee, move, Alt-duplicate, resize handles), Direct Selection, Type (draw frame, click caret, select, type), Rectangle/Ellipse/Polygon (+ frame variants), Line, Hand, Zoom.
 - PDF export (krilla): real selectable text with embedded font subsets, DeviceCMYK/RGB + spot Separations, bleed boxes, crop/bleed marks + page info, pages or spreads, PDF/A-2b (PDF/X-4 output intent pending) — `file.exportPdf`, File › Export PDF…, `designcraft-cli run --export out.pdf`. File › Export PDF… now opens an "Export PDF" options dialog (General / Compression / Marks and Bleeds / Advanced) and remembers the last-used settings across exports and sessions.