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>

server/routes/live.js

@@ -0,0 +1,46 @@
+const express = require('express');
+const { requireAuth } = require('../auth');
+const liveProjection = require('../services/liveProjectionService');
+
+const router = express.Router();
+
+function serializeState(state) {
+    return {
+        status: state.status,
+        stale: state.status !== 'success',
+        startedAt: state.started_at,
+        completedAt: state.completed_at,
+        inputHash: state.input_hash,
+        projectedCount: state.projected_count,
+        error: state.error
+    };
+}
+
+router.get('/channels', requireAuth, async (req, res) => {
+    const sourceId = req.query.sourceId === undefined ? null : Number(req.query.sourceId);
+    if (sourceId !== null && (!Number.isInteger(sourceId) || sourceId <= 0)) {
+        return res.status(400).json({ error: 'sourceId must be a positive integer' });
+    }
+    if (req.query.includeHidden !== undefined && !['true', 'false'].includes(req.query.includeHidden)) {
+        return res.status(400).json({ error: 'includeHidden must be true or false' });
+    }
+    const includeHidden = req.query.includeHidden === 'true';
+
+    try {
+        let state = liveProjection.projectionState();
+        if (state.status !== 'success') state = liveProjection.rebuild();
+        const channels = liveProjection.getChannels({ sourceId, includeHidden, userId: req.user.id });
+        return res.json({ projection: serializeState(state), channels });
+    } catch (error) {
+        console.error('[LiveProjection] Failed to serve projected channels:', error.message);
+        const state = liveProjection.projectionState();
+        return res.status(503).json({
+            projection: serializeState(state),
+            channels: [],
+            error: 'Live channel projection is unavailable'
+        });
+    }
+});
+
+module.exports = router;
+module.exports.serializeState = serializeState;