feat: brain-engine + brain-ui + docs — template full stack standalone

- brain-engine: server, embed, search, RAG, MCP, start.sh (standalone)
- brain-ui: source React complète, build.sh, DocsView avec tier colors
- docs: 14 pages guides humains (getting-started, architecture, sessions, workflows, agents, vues tier)
- brain-compose.yml v0.9.0: tier featured ajouté, sessions/agents par tier, coach_level, API key schema
- DISTRIBUTION_CHECKLIST v1.2: brain-engine + brain-ui + docs dans la checklist

brain-engine/queries/cold-start-kpi.sql

@@ -0,0 +1,30 @@
+-- cold-start-kpi.sql — KPI North Star : NO HANDOFF productif < 2 min
+-- Ref : brain-constitution.md §3
+-- Usage : sqlite3 brain.db < brain-engine/queries/cold-start-kpi.sql
+
+-- Vue globale
+SELECT
+    total_no_handoff,
+    passes,
+    pass_rate_pct || '%' AS pass_rate,
+    CASE
+        WHEN pass_rate_pct >= 80 THEN '✅ Layer 0 stable'
+        WHEN pass_rate_pct >= 60 THEN '⚠️  Layer 0 à surveiller'
+        ELSE '🔴 Layer 0 insuffisant — enrichir brain-constitution.md'
+    END AS verdict
+FROM v_cold_start_kpi;
+
+-- Détail par session
+SELECT
+    sess_id,
+    date,
+    CASE cold_start_kpi_pass
+        WHEN 1 THEN '✅ pass'
+        WHEN 0 THEN '❌ fail'
+        ELSE '— non mesuré'
+    END AS kpi,
+    notes
+FROM sessions
+WHERE handoff_level = 'NO'
+ORDER BY date DESC
+LIMIT 10;