docs(weekly): publish 2026-W39 report

[XiaoSeS]

What

• add the 2026-W39 weekly report to the official mirror
• update the weekly archive index and latest-report pointer
• record standalone source commit 7744c351ce943fd990871c7296217ca04913f77b

Why

Publish the verified W39 report on the official SkillHub documentation site after observation-site validation.

How

Copied site/ content byte-for-byte from the authoritative XiaoSeS/skillhub-weekly report commit. Existing assets/ and scripts/ already matched and required no changes.

Testing

• python3 scripts/sync_report_theme.py site/reports/*/index.html
• python3 scripts/build_site.py
• python3 scripts/validate_site.py _site
• official VitePress output assembly and weekly validation
• full site/, assets/, and scripts/ directory comparison against the standalone source
• sensitive/local-path scan

Impact

Documentation-only change. No application runtime, API, database, or release artifact changes.

[XiaoSeS]

Superseded by #904, which preserves the same content while adding the required DCO sign-off without rewriting the pushed branch history.