ai: rich-output blocks via lazy-fetched typed-fence protocol

Assistant replies can now emit typed fenced blocks that render as
@crema/*-ui components inline at their position in the reply.

- message-body.tsx: segmented rendering — alternating prose chunks and
  block dispatch (was: all blocks appended at end). Renderers for kpi,
  table, chart-bar/-line/-donut/-spark, code, diff, flowchart, orgchart,
  steps, checklist, welcome, hint, plus the legacy card kinds.
- block-schemas.ts: single source of truth — BLOCK_INDEX (one-line
  purpose per kind, always in prompt) + SCHEMAS (full JSON shape +
  example, fetched on demand).
- admin-tools.ts: new get_block_schema(kind) tool the model calls once
  per kind per thread to fetch the exact schema. Keeps the always-on
  prompt small (~110 tokens vs ~400 inline).
- assistant.tsx: replaces the inline schema dump with the generated
  thin index.
- ai.tsx: empty-state preview button injects a synthetic assistant
  message exercising every block, for renderer/theme smoke-testing.
- console.css + ai.tsx: shrink ATLAS headline so it doesn't slip under
  the composer with the added preview button.
- tsconfig.json + app.css: wire lib-data-ui, lib-code-ui, lib-diagram-ui,
  lib-onboarding-ui as siblings.

Adding a new block kind = add the lib paths, add a renderer case, add
a schema entry. No prompt edits required.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/themes/console.css

@@ -187,10 +187,10 @@
 /* Empty-state oversize text — letter-spacing tracking is the whole point */
 [data-theme="console"] .console-empty-headline {
   font-family: var(--console-font-mono);
-  font-size: clamp(2.25rem, 5.5vw, 4.5rem);
+  font-size: clamp(1.5rem, 3.2vw, 2.5rem);
   font-weight: 500;
   letter-spacing: 0.02em;
-  line-height: 0.95;
+  line-height: 1;
   color: var(--console-text);
 }
 
@@ -325,10 +325,18 @@
   color: var(--console-muted-2);
 }
 
-/* Header strip — session card */
+/* Header strip — session card. Solid background so messages scrolling past
+ * don't bleed through the sticky bar. */
 [data-theme="console"] .console-header {
   border-bottom: 1px solid var(--console-rule-soft);
-  background: linear-gradient(to bottom, oklch(0.16 0.02 240 / 0.6), transparent);
+  background: var(--console-ink);
+  -webkit-backdrop-filter: blur(12px) saturate(140%);
+  backdrop-filter: blur(12px) saturate(140%);
+}
+@supports ((backdrop-filter: blur(1px)) or (-webkit-backdrop-filter: blur(1px))) {
+  [data-theme="console"] .console-header {
+    background: oklch(0.13 0.02 240 / 0.82);
+  }
 }
 [data-theme="console"] .console-session-id {
   font-family: var(--console-font-mono);