fix(janus): Set playoutDelayHint=0 for Chrome to fix 1 FPS slowlink issue

[Dobbs3313]

Summary

Fixes the 1 FPS WebRTC H.264 streaming issue on Chrome/Blink browsers after the uStreamer 6.47 update.

Problem

After upgrading to v4.144, Chrome browsers experience:

• Video stuck at 1 FPS
• Constant 'slowlink' messages from Janus
• Works fine on Firefox

Related issue: #1632

Root Cause

Chrome's H.264 decoder doesn't handle uStreamer 6.47's new FPS limiter frame pacing well, causing RTCP feedback delays that trigger Janus slowlink detection.

Solution

Set playoutDelayHint=0 on video receivers for Chrome/Blink browsers when adding video tracks. This is similar to the existing Firefox workaround for playout-delay issues.

The playoutDelayHint property was already used in a commented-out block (removed in the refactoring commit ac0eee9f), but only for all browsers. This PR applies it specifically to Chrome/Blink where it's needed.

Changes

• Added Chrome/Blink detection when adding video tracks
• Set playoutDelayHint=0 on video receivers to reduce latency and fix frame timing
• Added logging for debugging

Testing

This fix should:

1. Allow Chrome to receive WebRTC H.264 at full frame rate
2. Eliminate constant slowlink messages
3. Not affect Firefox or Safari behavior

[Dobbs3313]

After further debugging, I found the actual root cause - it was not related to playoutDelayHint.

The issue was IPv6 in Janus. When ipv6 = true in janus.jcfg, Janus binds to multiple IPv6 interfaces (including Tailscale, link-local, etc.), which causes UDP packet loss and the "slowlink" warnings.

Evidence - Janus was binding to 7 different addresses:

UNCONN 0      0                              100.x.x.x:22950      0.0.0.0:*    (Tailscale IPv4)
UNCONN 0      0                             10.0.0.209:32455      0.0.0.0:*    (LAN IPv4)
UNCONN 0      0      [2601:xxxx:...]:20243                        [::]:*       (Public IPv6)
UNCONN 0      0      [fe80::xxxx...]%eth0:27509                   [::]:*       (Link-local)
UNCONN 0      0      [2601:xxxx:...]:24824                        [::]:*       (Public IPv6)
UNCONN 0      0      [fd7a:xxxx:...]:34070                        [::]:*       (Tailscale ULA)
UNCONN 0      0      [fe80::xxxx...]%tailscale0:25888             [::]:*       (Tailscale link-local)

The fix: Set ipv6 = false in /etc/kvmd/janus/janus.jcfg

Closing this PR and will file a new issue about the IPv6/multi-interface Janus configuration.