feat(M7): pages, Liquid Glass dock + UI library

[pedrobritx]

Milestone 7, built against the three supplied Apple PencilKit / iOS-style design frames: the Liquid Glass UI library, the bottom drawing dock, the color picker, multi-page boards, and a light/dark theme toggle.

What's in it

@notux/ui — Liquid Glass library (was an empty stub)

• Theme system (useTheme/applyTheme/getInitialTheme): light + dark token sets on [data-theme], persisted to localStorage, defaulting to OS preference; applied before first paint (no flash).
• Glass primitives: GlassPanel, GlassButton, Popover (portal + speech-bubble tail), Sheet (bottom sheet on narrow screens), Segmented, Slider (opacity track), Swatch (rainbow-ring variant).
• Faithful SVG instruments (pen, fineliner, highlighter, eraser, pencil, marker) that lift when active.
• Single design-system stylesheet exported as @notux/ui/styles.css.

Dock (Frames 1 & 2)

• Bottom-centered glass dock replaces the old left ToolPalette: instruments + rainbow color swatch + a "+" tray (select / shapes / text / import / theme toggle).
• Per-instrument settings (dockStore): each instrument remembers its color, width and opacity and pushes resolved values into toolStore so the canvas tools pick them up. The active instrument lifts; tapping it opens a width-preset + opacity popover.

Color picker (Frame 3)

• Grid + Sliders tabs, opacity slider, saved swatches (persisted to localStorage), and the EyeDropper API where supported. (Spectrum tab intentionally omitted per the agreed scope.)

Pages

• Synced ordered page list in the Yjs doc (packages/sync/src/pageList.ts) with seeding that migrates existing single-page boards (keeps page-0 content selectable).
• pageStore mirrors shapeStore's Yjs-binding/revision pattern; the active page is local per-user. Board threads the active pageId into CanvasStage/SelectionInspector; a navigator pill + tray handles add / switch / rename / delete / reorder.

Stroke pipeline

• Added opacity + style to ToolOptions / YStroke / DraftStroke; PenTool writes them; StrokeRenderer / OverlayLayer apply style-specific paint (highlighter = multiply) without double-applying the Group opacity already handled in ShapesLayer. The old highlighter ×4 size hack is removed (widths are now WYSIWYG).

Theming

• Theme tokens moved into the UI library; Konva layers read theme colors via a small cssVar() helper and re-render on toggle. Inspector + home restyled to tokens.

Scope decisions (confirmed with the requester)

• Light + Dark with a toggle • Faithful SVG instruments • Ruler omitted this milestone • Faithful color picker (Grid + Sliders, no Spectrum).

Verification

• ✅ pnpm -r typecheck — all 5 packages clean.
• ✅ pnpm build — full production build succeeds (Vite, 340 modules; @notux/ui CSS bundled).
• ✅ Page-list logic (compiled with tsc, run on Node against real yjs): fresh-seed, idempotent seeding, migration of existing page-0 boards, multi-page migration, add / rename / reorder / delete (delete also drops the page's shapes), and cross-Y.Doc replication (the multiplayer path). 11/11 pass.
• ✅ Dock state machine (compiled, run on Node): selectInstrument pushes the resolved preset into toolStore; per-instrument color/width/opacity memory survives switching; eraser → eraser tool; highlighter width is no longer ×4. 10/10 pass.

⚠️ No browser/visual verification. This sandbox has no Chromium and no Playwright/headless browser, so the rendered dock, popover, color picker, page navigator and the theme toggle have not been smoke-tested visually. Recommend a manual pnpm dev pass (open /board/<id>) before marking ready for review — in particular: dock layout vs. the frames, popover/sheet positioning, and the light↔dark flip.

Notes

• A Page type / DB table already existed but was unused; this PR syncs page metadata via Yjs (consistent with how shapes sync). Server-side page persistence and live page thumbnails are left as follow-ups.
• ToolPalette.tsx and its CSS were removed (superseded by the dock); its image/PDF import logic moved into the dock's "+" tray.

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