Filter pills by backend tags (slug membership), drop keyword matching

Replace the keyword/source-majority Interest system with a StoryPill enum that
matches stories by canonical category slugs. StorySummary gains a tolerant
tags[] (optional, decode-safe); effectiveTags uses tags, falling back to topic
during the backend transition. No more headline keyword-searching on the client —
the backend decides classification; the client asks slug membership.

Pills: All, F1, Sport, AI, Cloud, HomeLab, Tech, Uganda, South Africa, Canada, US.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Jarvis/Views/Home/StoryRowView.swift

@@ -117,7 +117,7 @@ struct StoryRowView: View {
             StoryRowView(
                 story: StorySummary(
                     id: "\(score)", headline: "Bank of Uganda cuts interest rates by 50 basis points",
-                    summary: "", topic: "finance", signalScore: score, scoreBreakdown: breakdown,
+                    summary: "", topic: "finance", tags: ["finance"], signalScore: score, scoreBreakdown: breakdown,
                     sourceCount: 7, sources: sources, consensus: nil, conflict: nil,
                     updatedAt: Date().addingTimeInterval(-3600), createdAt: Date()),
                 isCached: score == 64