feat: add saved market bookmarks

[pq198363-ops]

Closes #364

Summary

• add a persisted useBookmarksStore for saved market IDs
• add an accessible BookmarkButton with pressed state and save/remove labels
• wire saved market controls into the marketing widget header with an expandable saved list
• document the client-side saved market behavior

Validation

• node node_modules/jest/bin/jest.js --runTestsByPath app/state/__tests__/bookmarks.test.ts app/components/__tests__/BookmarkButton.test.tsx app/(marketing)/_components/__tests__/markets-widget.test.tsx --runInBand - 8 tests passed
• node node_modules/eslint/bin/eslint.js app/components/BookmarkButton.tsx app/components/__tests__/BookmarkButton.test.tsx app/state/bookmarks.ts app/state/__tests__/bookmarks.test.ts app/(marketing)/_components/markets-widget.tsx app/(marketing)/_components/__tests__/markets-widget.test.tsx - passed
• git diff --check - no whitespace errors; only Git line-ending warnings on Windows

Type-check note

• node node_modules/typescript/bin/tsc --noEmit --pretty false still fails on existing unrelated files such as ResolutionPreview, ErrorBoundary, wallet modal typing, badge variant typing, PredictionCard, and components/ui/dialog.tsx; no reported errors point to this PR's new bookmark files or the updated marketing widget.

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