Peer media (music/video) wouldn't play: the frontend downloaded the whole
file via RPC as base64 and made a non-seekable Blob URL, so <video>/large
<audio> stalled and big files hit the RPC timeout.
Add GET /api/peer-content/<onion>/<id> — a same-origin, session-gated proxy
that forwards the browser's Range header to the peer's /content/<id> (which
already returns 206 Partial Content) and passes status + Content-Range +
Content-Type back. PeerFiles.playMedia() now points <video>/<audio> at this
streaming URL for free content instead of buffering a base64 blob, so the
player can seek and start immediately. Onion/id validated to prevent
SSRF/path traversal. (Paid preview keeps its existing flow.)
Verified: cargo build --release EXIT 0; vue-tsc --noEmit EXIT 0.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>