docs: finish launch journey and metadata

[abrichr]

What changed

• finishes the canonical local, Desktop, Cloud, qualification, sealing, and security-review journeys
• documents the shipped openadapt flow seal command and corrects the recording-to-attested-bundle Cloud handoff
• adds useful redirects and canonical metadata for legacy package routes
• gives key launch pages distinct search metadata and routes public calls to action to their canonical destinations
• fixes dark-mode footer readability, preserves the working mobile navigation, and aligns component lifecycle/version references

Verification

• UV_CACHE_DIR=/private/tmp/uv-cache-docs uv run --locked --extra dev pytest tests/ -q (101 passed)
• UV_CACHE_DIR=/private/tmp/uv-cache-docs uv run --locked --extra dev python scripts/validate_docs.py
• UV_CACHE_DIR=/private/tmp/uv-cache-docs uv run --locked --extra dev python scripts/check_published_version_claims.py --offline
• UV_CACHE_DIR=/private/tmp/uv-cache-docs uv run --locked --extra dev mkdocs build --strict
• Playwright at 320x568, 390x664, and 390x844: no horizontal overflow and final mobile-nav link remains reachable
• footer contrast: light text/link 7.92:1/5.98:1; dark text/link 11.51:1/11.07:1