fix(media): stabilize reconnects and quality recovery

[TNTcraftHIM]

This maintenance phase corrects connection and media recovery after startup deadlines, congestion and packet loss. Route selection remains a bounded operation; Pion and LiveKit continue to own congestion control, adaptation and retransmission.

Changes stay within existing owners:

• Preserve an untried SFU fallback when a connected P2P candidate produces no first frame before its deadline. Retire expired native preparations using the current edge identity.
• Correct paced output, probe accounting and partial-recovery demand. Negotiate RTX consistently for native forwarding and SFU publication, including repaired stream identifiers for simulcast.
• Return working IPv4 mappings without waiting for optional IPv6 work, and separate NAT observations by the local socket/address that produced them.
• Keep optional App availability separate from basic source selection; stabilize nickname/chat layouts and restore volume from zero correctly.
• Retry complete Gitee reads, including response bodies and hash verification. Ambiguous uploads remain single attempts and are reconciled against the remote inventory before rerunning.

Related: #468, #464, #471. The repairs affect paths discussed in these reports; incomplete field diagnostics do not establish that each report has the same cause, so this PR does not automatically close them.

Validation

• Web type checks, production build and 1,624 tests passed. Go core, formatting, vet and local target builds passed.
• Delayed RTX recovery reproduced the defect before the fix; the repaired-SSRC mutation also fails the focused regression. Real Windows H.264 and VP8 capture passed the SFU gates, including settings, reload recovery and retirement.
• The media lifecycle gate passed all 14 trials across Browser/App pairings and P2P/SFU handoffs. Native connectivity, paced forwarding and negative-control checks passed.
• Responsive UI and current website architecture links were checked; Gitee's current release was independently downloaded and matched against the GitHub originals.
• Platform candidate: all five Apps, both Server architectures and container checks passed at c534573b. Subsequent tracked changes only update documentation, the complete-matrix CI budget and race-test coverage.
• Full network comparison completed 70 trials before the batch's 45-minute limit. The remaining scenario passed three paired repetitions; all 71 scenario/setting variants are covered, with 58 media and 13 expected/observed unavailable outcomes. Six negative controls passed, and owned resources were cleaned up. These are controlled observations, not a public success rate.
• The final validation also includes the shared forwarder under the Go race detector. The separate sole-active-output publication experiment still shows inconsistent recovery: two of four current-code repeats did not pass its recovery observation, so the limitation below remains open.

The native SFU allocator still has a measured recovery limitation when only its lowest rate-controlled encoding is active. Fixing that requires a supported upstream demand input; no second controller or allocator fork is introduced. Unmatched capture-failure reports and physical-platform coverage retain their documented evidence limits.

Release notes

中文

这是一次连接与播放稳定性更新，重点改善重连、弱网后的画质恢复和下载镜像可靠性。与 Piik 2.0.0 保持兼容。

• 修复连接等待超时后过早跳过备用线路的问题，保留尚未尝试的媒体服务器兜底机会。
• 改善原生分享在网络拥塞后的画质恢复，并修复转发和媒体服务器发布链路上的视频重传协商遗漏。
• 修复原生观看准备超时后的清理与重试，以及音量从零恢复时的异常。
• 避免可选的 IPv6 端口映射拖慢 IPv4 准备，并修正多网卡环境下的 NAT 预测观测归属。
• 修复昵称编辑、聊天字数变化引起的布局移动；保持 App 提示简洁，并为更新提示补充官网备用下载入口。
• 修复 Gitee 镜像同步在传输中途断开时未重试的问题，校验通过后才完成镜像发布。

仍在跟进：部分原生媒体服务器链路的弱网后恢复仍可能偏慢；尚缺匹配诊断的采集失败反馈不能确认已解决。

English

This maintenance update improves connection and playback recovery after interruptions and congestion, along with download-mirror reliability. It remains compatible with Piik 2.0.0.

• Preserve untried media-server fallback routes when a connection reaches its waiting deadline.
• Improve native sharing quality recovery after congestion and fix missing video retransmission negotiation in forwarding and media-server publication paths.
• Correct cleanup and retry after native viewing preparation expires, and restore playback volume correctly from zero.
• Prevent optional IPv6 port mapping from delaying IPv4 preparation, and associate NAT-prediction observations with the correct local interface.
• Stabilize nickname editing and chat counters, keep App guidance unobtrusive, and add the website's alternate downloads to update notices.
• Retry interrupted Gitee mirror transfers and complete publication only after verification succeeds.

Still under investigation: recovery after congestion can remain slow on some native media-server paths. Capture-failure reports without matching diagnostics are not claimed as resolved.