Adds a discreet "Quellen & Lizenzen" link to the SDK sidebar footer
(below the existing Export button) pointing to the /sdk/licenses page
shipped in commit dfac940.
Part of Task #24 (AGB/Impressum audit) — the legal mandate that
attribution be discoverable for every output is now satisfied at
three layers:
- platform-wide overview reachable from every SDK page (this commit)
- per-export footer in compliance PDFs (commit 07cc00d)
- inline source badge per control via <SourceBadge> (commit dfac940)
Benjamin Admin
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