Return the AlvenX header to top while preserving Demo state

[AlbertXXuu]

The AlvenX wordmark now returns the current Demo document to its true top using the shared native-button contract. Pointer, Enter and Space preserve the current saved result, expanded details, URL/hash and history. Activation at the top does nothing, and reduced motion scrolls immediately.

The controlled CSS copy and provenance adopt shared home-navigation revision 2026-09-04.1. The wordmark and header geometry stay unchanged. This follows the separately completed English Demo in PR #4 and leaves all raw experiment evidence intact.

Validation:

• Full pnpm check passed: 80/80 unit/process tests, 4/4 browser tests, brand, format/lint/types, historical and recorded evidence verification.
• Extended existing browser coverage for both motion preferences and all three activation methods, state retention, document lifetime, top activation, focus and 390/900/1440 px geometry.
• pnpm package:smoke passed.
• Independent Git export of 5365f23: frozen installation, brand verification and 4/4 browser tests passed.
• Parent brand/workspace validators passed (22 assets, five README and header-navigation registrations, five repositories).
• Actual local Demo: scrollY changed from 496 to 0 while its existing query/hash, saved 20+20 run and independent verification remained unchanged; header height 74.4844 px and wordmark width 160 px.
• Independent read-only review passed.

SPIKE_CONDITIONAL remains unchanged. Merged as 86b7c9a, with clean D-drive main matching origin/main and the tested source tree. PR CI passed: https://github.com/AlbertXXuu/ReproLock/actions/runs/33891785629. Main CI passed: https://github.com/AlbertXXuu/ReproLock/actions/runs/33893139520. Both Node matrix jobs passed all steps. The first PR Node 24 attempt was cancelled after approximately ten minutes reported in browser installation; its completed log showed installation and tests recovered before cancellation took effect, leaving packaging incomplete. One same-commit Node 24 retry then passed the full job. The original snapshot/log and both final CI receipts are preserved in the local AlvenX audit; no checks were weakened or removed.