Use English across the Demo and align AlvenX branding

[AlbertXXuu]

The Demo now uses English consistently across its interface, accessible labels, execution states, error messages, documentation references, and README screenshot. Stored execution results remain explicitly labeled as saved evidence; this language update does not imply a new experiment or a product-stage promotion.

This PR also preserves the separately authorized AlvenX brand handoff in two commits: the shared README descriptor contract and the canonical centered wordmark with matching provenance. The English UI implementation and acceptance receipt follow in separate commits.

Validation completed locally:

• Full pnpm check: 80 unit/process tests and 4 browser tests passed, with formatting, lint, type, brand, and evidence checks.
• pnpm package:smoke: passed.
• Actual browser acceptance at 390, 900, and 1440 px: English content, no horizontal overflow, local resources loaded, and header geometry matched the preserved accepted Studio reference.
• Independent Git export at 0e02daca5b4aab4c6a5b02e876aa10480f243849: frozen pnpm installation, brand verification, and 4 browser tests passed.
• Shared AlvenX brand and workspace validators passed.
• Independent read-only review found no remaining blockers.
• Of 250 protected files, 247 remained byte-identical; only the approved wordmark, its provenance, and the English README screenshot changed. Raw experimental reports, frozen tests, runner behavior, and historical evidence remain unchanged.

The product gate remains SPIKE_CONDITIONAL, with product value still unproven. PR CI passed on 52c1819: https://github.com/AlbertXXuu/ReproLock/actions/runs/33890143146. Merged as 5b16d22; main CI passed: https://github.com/AlbertXXuu/ReproLock/actions/runs/33890395310. Both runs passed Node 22.23.2 and 24.20.0. The fixed D-drive checkout is clean on main and matches origin/main and the tested PR tree. The local integration receipt and CI job details are preserved in the AlvenX workspace audit for this follow-up.