feed: Phase 2 fanout via outer product — activities ∘.× audience, flatten, edge-guard, dedupe + 29 tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/feed/conformance.sh

@@ -13,7 +13,7 @@ if [ ! -x "$SX_SERVER" ]; then
   exit 1
 fi
 
-SUITES=(basic)
+SUITES=(basic fanout)
 
 OUT_JSON="lib/feed/scoreboard.json"
 OUT_MD="lib/feed/scoreboard.md"
@@ -31,6 +31,8 @@ run_suite() {
 (load "lib/feed/normalize.sx")
 (load "lib/feed/stream.sx")
 (load "lib/feed/api.sx")
+(load "lib/feed/fanout.sx")
+(load "lib/feed/dedupe.sx")
 (epoch 2)
 (eval "(define feed-test-pass 0)")
 (eval "(define feed-test-fail 0)")