Rebuild Wave learning documentation and complete translations for all nine locales

[LunaStev]

The documentation now provides a guided Wave course with runnable examples, explanations, exercises, and worked answers. All 54 pages are available in the nine supported locales (486 pages total), so readers can follow the same course and references in their selected language.

• Consolidate lessons under language/, add four practical projects, and expand the standard library reference with imports, errors, ownership, and platform requirements.
• Give the standard library its own navigation tab, move toolchain material into Whale, remove the design-goals page, and redirect retired URLs. Archive retired official catalogue entries while preserving revisions and independently authored documents.
• Use the official Windows installer and preserve readable multiline code, commands, and expected output across translations. Translations use Google-assisted drafts with technical terminology and semantic corrections.
• Preserve the latest master changes for Whale typed calls and format 2 interchange and synchronize the corresponding translations.
• Add example and translation checks, and cover all locales in publication and SEO tests while retaining explicit fallback tests.

Validation:

• Translation coverage, code fences, Markdown structure, example IDs, and internal links: passed for 432 translations.
• All 134 marked Wave examples were validated against a matching compiler/std snapshot during the documentation work; their code and manifest are unchanged in this PR.
• go test ./internal/document ./internal/web ./internal/web/handler
• Frontend typecheck, documentation navigation tests, SEO tests, and production build.
• git diff --check

Documentation is embedded in the application binary. Publishing the new pages requires the usual application rebuild and restart; this PR does not deploy the site.