feat: add grid preference migrations

[fabric0de]

Summary

• Add explicit, sequential, forward-only migrations for persisted grid preferences.
• Integrate migrations with parseGridPreferences and readGridPreferences.
• Reject incomplete, duplicate, malformed, unsupported, future, or throwing migration chains safely.
• Preserve the existing normalization of column visibility, sizing, ordering, pinning, and grid density.
• Re-export the preference migration APIs from the React, Vue, and Svelte UI packages.
• Add task-oriented documentation for preference storage, schema upgrades, storage-key decisions, and column allowlists.

Public API

• Add GridPreferencesMigration.
• Add GridPreferencesParseOptions.
• Add migrateGridPreferences(value, migrations).
• Extend parseGridPreferences(value, options) with migration support.
• Extend readGridPreferences(storage, key, options) with migration support.
• Re-export the new APIs from:
  • @open-grid/react-ui
  • @open-grid/vue-ui
  • @open-grid/svelte-ui

Behavior

• Migrations must be sequential and forward-only.
• Each migration result must match its declared target version.
• Missing migration steps reject the stored payload.
• Duplicate source versions reject the migration configuration.
• Unsupported target versions and future schemas are rejected.
• Exceptions thrown by product migrations are contained and return null.
• Migrated preferences are normalized against the current column allowlist.
• Sorting, filters, pagination, selection, focus, and editing remain excluded from persisted preferences.

Documentation

• Add docs/preferences.md.
• Update the React, Vue, and Svelte integration guides.
• Update architecture documentation and the public roadmap.
• Update README.md and CHANGELOG.md.

Verification

• Tests cover successful preference migrations.
• Tests cover missing, duplicate, malformed, unsupported, and throwing migrations.
• pnpm test && pnpm check passes.
• pnpm build passes.
• pnpm api:check passes.
• pnpm docs:build passes.
• Public API contracts are updated for all framework packages.
• pnpm benchmark:bundle:check passes all required package budgets.
• Primitives gzip is 13.97 KiB against a 14.65 KiB required limit.
• CHANGELOG.md is updated.
• No generated .benchmark-results/, .release/, credentials, or private data are included.