TASK 5 items 1-3: reusable stream, health banner, docs refresh

- Reusable stream: GetOrCreateReusableStreamAsync, cached via LayoutStore, bound at broadcast insert
- Health monitoring: GetStreamHealthAsync polls liveStreams.status, report-by-exception banner
- Go-live order: ensure stream → create broadcast → then start pump (URL must exist first)
- Full broadcast form scoped (TASK 5 items 6-7) in TASKS.md + ai.md
- TASK 23 trimmed to technical scope, TASK 26 added (marcom/launch kit)
- Confidential files: MONETIZATION.md + MARCOM.md (gitignored, not committed)
- .gitignore updated for confidential business files
- HANDOFF.md updated with session state and next steps

Services/StreamHealthReporter.cs

@@ -0,0 +1,26 @@
+using ytLive.Models;
+
+namespace ytLive.Services;
+
+/// <summary>Report-by-exception (TASK 5 item 3): turns liveStreams
+/// configuration issues into a banner. good/ok/noData and info-only issues
+/// produce no banner; the first warning/error issue produces its text, colored
+/// by the worst severity (error beats warning). Pure — fully testable.</summary>
+public static class StreamHealthReporter
+{
+    public static HealthIssueReport BannerFor(IEnumerable<StreamConfigurationIssue> issues)
+    {
+        var reportable = issues
+            .Where(i => i.Severity is StreamIssueSeverity.Warning or StreamIssueSeverity.Error)
+            .ToList();
+        if (reportable.Count == 0) return new HealthIssueReport(null, false);
+
+        var isError = reportable.Any(i => i.Severity == StreamIssueSeverity.Error);
+        return new HealthIssueReport(
+            string.Join(", ", reportable.Select(i => i.Type).Where(t => !string.IsNullOrWhiteSpace(t))),
+            isError);
+    }
+}
+
+/// <summary>null Text = no banner. IsError colors it: error → app red, else amber.</summary>
+public record HealthIssueReport(string? Text, bool IsError);