Four polish improvements aimed at production-floor usability.
1. Empty-state placeholder for the participants card. When Participants.Count == 0, the DataGrid is hidden in favor of a friendly 'Waiting for Teams' panel: faded dragon mark, headline, explainer, and a four-item checklist (Teams running? NDI broadcast on? Discovery group correct? Firewall clear?). New CountToVisibilityConverter (with optional 'empty' parameter to invert) drives both the placeholder and the DataGrid visibility from the same Participants.Count source.
2. Per-pipeline error / no-signal surfacing. IsoHealthStats grows an init-only State property populated from IsoPipeline.State. ParticipantViewModel.UpdateStats maps that to a StateLabel ('LIVE' / 'NO SIGNAL' / 'ERROR' / 'STARTING' / '—'). The ISO toggle button gains DataTriggers on StateLabel — coral-tinted '● ERROR' when the supervisor gives up, amber-tinted '● NO SIGNAL' when the slate threshold trips. Operators can see at a glance which pipelines are broken.
3. JetBrains Mono Variable v2.304 (OFL) bundled at Assets/Fonts/JetBrainsMono.ttf. Wd.Font.Mono now points at the embedded font so machine names, timecodes, and stat counters render in JetBrains Mono regardless of system fonts. Falls back to Cascadia Mono / Consolas if the resource is missing.
4. Tooltip pass over every interactive control in the settings panel (framerate / resolution / aspect / audio / discovery group / output group / hide-local checkbox / Apply button / per-row Output Name textbox / per-row ISO toggle). Operators learn affordances on hover instead of by trial and error.
Tests: 76/76 unit + 9/9 NDI integration green.
Adds an NdiGroupSettings record carrying optional comma-separated NDI group lists for the finder and the senders. Extends INdiInterop.CreateFinder / CreateSender with optional groups arguments and populates NDIlib_find_create_t.p_groups and NDIlib_send_create_t.p_groups via P/Invoke. IsoController reads the settings on construction, threads DiscoveryGroups into NdiDiscoveryService and OutputGroups into IsoPipelineConfig, and exposes SetGroupSettingsAsync for runtime updates (group changes apply on next process restart so live pipelines aren't orphaned).
This unblocks the 'transcoder' topology where Teams broadcasts NDI on a private group (e.g. teamsiso-input) and TeamsISO re-emits clean normalized streams on Public — keeping raw, wrong-framerate Teams sources off the production network.
EngineConfig schema is JSON-back-compat: existing config.json files (no NdiGroups field) deserialize with NdiGroups=null and load as NdiGroupSettings.Default. UI surface for these settings comes in a follow-up.
Tests: 72/72 passing (was 69) — added IsoController coverage that group settings are read from ConfigStore on startup, passed to the finder, threaded into per-pipeline config, and round-trip through SetGroupSettingsAsync/Save/Load.
