HydraIssues

Sub-issue of #565 (master: HydraNPS end of experience rating). Full design on #565. This issue is Phase 5b: browser path alignment in hydraneckwebrtc.

Scope:

• Add score_scale: "10-half-star" to the OnSessionEnd NPS submission (internal/client/nps.go) so the dashboard can split head vs browser sources
• No UI change to the existing inject.go widget
• Note: SubmitNPS already accepts 200 and 201, so hydranps upsert semantics are compatible

Reminder that motivated the metric split: the browser overlay opens on RTCPeerConnection disconnect, so browser scores on non-quit end reasons rate a broken stream; hydranps excludes them from the NPS numbers (handled service side in the Phase 1 sub-issue).

Depends on: hydranps sub-issue.