release: prepare v4.5.0

[Dastari]

Summary

• bump data-table-pro from 4.4.0 to 4.5.0 and commit the generated distribution artifacts
• add public scrollbar visibility control and keep both scrollbar axes plus their corner above fixed columns and pinned rows
• create a visibility-aware internal fill spacer so dynamically visible fixed-width columns keep their configured widths, including grouped and virtual tables
• update the changelog, README installation guidance, API reference, migration guide, roadmap baseline, demo fixture, API snapshot, and browser regressions

Root cause

The scrollbars did not establish a stacking layer above sticky table regions. Fill layout also treated the last visible fixed data column as flexible; although the reserved spacer was already recognized by ordering, export, clipboard, and interaction paths, no internal spacer column was created from the current visible leaf set.

Impact

Consumers can opt into persistent scrollbars with scrollbarVisibility="always". Fixed-width fill tables now retain their configured widths as column visibility changes, place unused space before right-pinned actions, and preserve horizontal overflow rather than compressing columns. Consumers do not need to define or reference __spacer__.

Validation

• pnpm test:coverage — 317 tests passed
• pnpm lint
• pnpm typecheck
• pnpm demo:typecheck
• pnpm build
• pnpm api:update && pnpm api:check
• pnpm test:consumer
• pnpm bundle:check
• pnpm demo:build
• pnpm audit — no known vulnerabilities
• standalone TypeScript check for browser-tests/data-table.spec.ts

The browser regressions were added and typechecked. Local Chromium execution remains unavailable in this container because the host is missing libnspr4.so; CI should execute the Playwright suite.