content: content/* API facade + 26 tests (Phase 1 complete, 133/133)

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

lib/content/conformance.sh

@@ -15,7 +15,7 @@ if [ ! -x "$SX_SERVER" ]; then
   fi
 fi
 
-SUITES=(block doc render)
+SUITES=(block doc render api)
 
 OUT_JSON="lib/content/scoreboard.json"
 OUT_MD="lib/content/scoreboard.md"
@@ -36,6 +36,7 @@ run_suite() {
 (load "lib/content/block.sx")
 (load "lib/content/doc.sx")
 (load "lib/content/render.sx")
+(load "lib/content/api.sx")
 (epoch 2)
 (eval "(define content-test-pass 0)")
 (eval "(define content-test-fail 0)")