Unify English and German README documentation

[patrickschiller]

Summary

• align the English and German README structure, section order, technical examples, and commands
• add missing German product and provenance context and keep client-specific capability wording consistent
• carry verified details that previously appeared in only one language into both versions, including local capture-date semantics, Azure frontmatter fields, native Markdown examples, and optional API configuration
• clarify local MCP use in Codex versus the private Secure MCP Tunnel currently required by ChatGPT

Impact

Documentation only. This does not change browser permissions, GitHub scopes, network endpoints, archive formats, deletion behavior, storage, or credential handling. No private archive or website content is included.

Verification

• ✅ README parity and local-link validation
• ✅ git diff --check
• ✅ node --test tests/capture-utils.test.js — 15/15 passed
• ⚠️ python3 -m unittest discover -s tests -p "test_*.py" — 35/36 passed; the unchanged iOS release test expects build 6, while the unchanged Xcode project on current main reports build 9