feat: precompute stream grouping during source sync (#13)

Move variant grouping work out of Live TV rendering into the
catalog pipeline: a liveProjectionService builds the logical channel
projection (schema in liveProjectionSchema) whenever a source is
added, synced or modified (name change, new address), and the
projection is served through a /live route. ChannelList now consumes
the precomputed projection via a liveChannelProjection client
service, recalculating only when the catalog changes. Cover
projection building, incremental recompute and client consumption
with tests.

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

public/js/services/liveChannelProjection.js

@@ -0,0 +1,50 @@
+(function (root, factory) {
+    const service = factory();
+    if (typeof module === 'object' && module.exports) module.exports = service;
+    if (root) root.LiveChannelProjection = service;
+})(typeof globalThis !== 'undefined' ? globalThis : this, function () {
+    function mapResponse(response, sources = []) {
+        if (!response || !Array.isArray(response.channels)) {
+            throw new Error('Invalid live channel projection response');
+        }
+
+        const sourceById = new Map(sources.map(source => [String(source.id), source]));
+        const favorites = new Set();
+        const hiddenItems = new Set();
+        const channels = [];
+
+        response.channels.forEach(logicalChannel => {
+            if (!logicalChannel || !Array.isArray(logicalChannel.variants)) return;
+            logicalChannel.variants.forEach(variant => {
+                const source = sourceById.get(String(variant.sourceId));
+                const id = String(variant.id);
+                const mapped = {
+                    ...variant,
+                    id,
+                    logicalId: logicalChannel.id,
+                    logicalFingerprint: logicalChannel.fingerprint || logicalChannel.id,
+                    logicalDisplayName: logicalChannel.displayName || logicalChannel.name,
+                    streamId: variant.streamId ?? id,
+                    tvgId: variant.tvgId ?? variant.epg_channel_id ?? null,
+                    tvgLogo: variant.tvgLogo ?? variant.streamIcon ?? variant.stream_icon ?? '',
+                    url: variant.url ?? variant.streamUrl ?? variant.stream_url ?? '',
+                    groupTitle: variant.groupTitle ?? variant.categoryName ?? variant.categoryId ?? 'Uncategorized',
+                    sourceType: variant.sourceType ?? source?.type ?? 'xtream',
+                    sourceName: variant.sourceName ?? source?.name ?? ''
+                };
+                channels.push(mapped);
+                const key = `${mapped.sourceId}:${id}`;
+                if (variant.isFavorite) favorites.add(key);
+                if (variant.isHidden) hiddenItems.add(`channel:${mapped.sourceId}:${mapped.streamId || id}`);
+            });
+        });
+
+        return { channels, favorites, hiddenItems, projection: response.projection || {} };
+    }
+
+    function canUse(response) {
+        return Boolean(response && Array.isArray(response.channels) && !response.projection?.stale);
+    }
+
+    return { canUse, mapResponse };
+});