feat(kumo): add ColorPicker component with parity UI and eyedropper

[singkia]

Summary

• add a new ColorPicker component to @cloudflare/kumo with parity UI/behavior from the production implementation
• support HEX/RGB/HSL/HSB editing flows with color area + hue slider controls
• include optional EyeDropper integration with capability detection and non-intrusive error handling
• keep external value protocol as hex while bridging internal Color object state for stable drag/edit interactions

Files

• packages/kumo/src/components/color-picker/* (new module: component, primitives, state bridge, tests, exports)
• packages/kumo/src/index.ts (main export)
• packages/kumo/vite.config.ts (component entry)
• packages/kumo/package.json + pnpm-lock.yaml (dependency + export path)
• .changeset/olive-ladybugs-type.md

Validation

• pnpm --filter @cloudflare/kumo typecheck
• pnpm --filter @cloudflare/kumo exec vitest run src/components/color-picker/color-picker.test.tsx
• pnpm --filter @cloudflare/kumo exec oxlint --config .oxlintrc.json src/components/color-picker src/index.ts --type-aware
• pnpm --filter @cloudflare/kumo exec eslint src/components/color-picker src/index.ts

Notes

• keeps visual/interaction parity while removing internal remount coupling in HEX input sync
• retains white thumb contrast ring with stable class usage (before:bg-white)

[singkia]

Updated this PR to keep the scope focused on ColorPicker.

What changed in this revision:

• rebased the branch onto the current main
• removed the unrelated feat(select): add grouped options compound API changes that had been mixed into this branch
• kept only the ColorPicker implementation, exports, package entry updates, and changeset

Validation I ran locally:

• pnpm --filter @cloudflare/kumo typecheck
• pnpm --filter @cloudflare/kumo build
• pnpm --filter @cloudflare/kumo test -- src/components/color-picker/color-picker.test.tsx
• pnpm --filter @cloudflare/kumo test:exports
• pre-push changeset validation via lefthook

So PR 174 should now represent only the ColorPicker work.