host: typed relations — Phase 6 (schema validation) + post-page perf fix

Phase 6 — gradual schema validation made real:
- host/blog-type-schemas now carries a declarative schema (a list of
  {:block :msg} required-element rules); "article" requires an h1.
- host/blog--all-tags / --schema-issues / host/blog-type-issues walk the parsed
  content and report each missing required block; host/blog-type-valid? = no
  issues. A type with no schema imposes nothing (gradual).
- seed an "article" type-post (article subtype-of type). edit-submit now lists
  the specific schema issues on a 400 ("an article needs a heading"), so a post
  that is-a article must satisfy it on save.

Post-page performance (the unresponsiveness): a post page was ~1s even with no
relations and no load — NOT CPU (render-page ~2ms, in-memory handler ~5ms) but
the DURABLE read path: host/blog--relation-blocks called host/blog-out/in, each
re-scanning the whole KV (host/blog-slugs + an all-edges scan), so a page did ~7
kv-keys performs deep in the call stack. Each durable perform routes through
cek_run_with_io and is costly there. Fixes:
- host/blog-out/in read DIRECT edges from the durable edge store (string scan),
  not lib/relations (whose queries re-saturate the Datalog ruleset, ~seconds).
- host/blog--relation-blocks reads the KV key list ONCE and derives both the post
  set and the edges in memory (host/blog--edges-for / --recs-slugs), one kv-keys
  plus a host/blog-get per linked post. Post pages: ~1s -> ~0.02s (46x); live
  11-135s -> ~0.15s. lib/relations stays for TRANSITIVE queries only.
- conformance timeout 300 -> 600s: the relations-heavy blog suite is CPU-bound
  under shared-box contention and was tripping a false truncation at 300.

271/271 (blog 100). Verified live: post pages fast, Tags/Related/Tagged-with-this
render, schema rejection works.

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

lib/host/conformance.sh

@@ -113,7 +113,10 @@ emit_eval () { echo "(epoch $EPOCH)"; echo "(eval \"$1\")"; EPOCH=$((EPOCH+1));
   done
 } > "$TMPFILE"
 
-OUTPUT=$(timeout 300 "$SX_SERVER" < "$TMPFILE" 2>&1 || true)
+# 600s: the blog suite drives the relations graph hard (every is-a/types-of/
+# instances-of query re-saturates the Datalog db), so it's CPU-bound and slower
+# under shared-box contention. 300s was tripping a false truncation.
+OUTPUT=$(timeout 600 "$SX_SERVER" < "$TMPFILE" 2>&1 || true)
 
 # Fail LOUD on any load/eval error. A test file that errors mid-load silently
 # truncates its suite — the runner returns only the tests that ran before the