docs: make all documentation bilingual, English first

[lweberru]

Summary

• Keep existing .md URLs as canonical English and add complete German .de.md companions for all 90 Markdown documents.
• Add reciprocal language navigation, locale-aware cross-page links and compatible heading anchors; document paired maintenance in contributor guidance.
• Cover Accelerator/module references, workflow catalogue, Configurator user/developer/design guides, operator runbooks and Assistant knowledge reading versions.
• Preserve generated Terraform contracts and all executable examples. The 19 machine-ingested English Assistant topics remain byte-identical; German companions are human-only and indexed separately.
• Regenerate only documentation-bound Assistant source fingerprints and the resulting catalogue bundle hash. No prompts, facts, application capabilities, workflow definitions or infrastructure are changed.

Validation

• 90/90 EN/DE pairs; 1,605 local links/fragments checked without errors.
• Legacy canonical heading anchors retained; all canonical fenced examples and 68 paired executable example blocks preserved.
• All 19 curated Assistant source hashes match the pre-translation baseline; generated Terraform blocks remain byte-identical.
• Pinned Node 24.21.0 / npm 11.19.0: complete npm run check passes, including provenance freshness, lint, build/type-check and 838 passing tests; 66 environment-dependent tests skipped.
• Final npm run assistant:check and git diff --check pass.

Boundaries

• Generator-owned technical reference tables intentionally remain unchanged in German guides; German introductions identify the canonical reference.
• No real-model qualification rerun: curated prompt text, selection and capabilities are unchanged. Existing qualification receipts do not certify the new provenance hash; protected release qualification remains mandatory for a future build.
• No cloud mutation, deployment or production approval.