docs: fix stale references, seed data case bugs, and convert ASCII diagrams to Mermaid

Audit all docs and examples against current codebase state. Fix seed_demo.sql
domain constant casing (IssuerType, TargetType, AgentStatus) that would cause
agent dispatch failures. Fix example docker-compose health endpoints (/health
not /api/v1/health) and env var names (CERTCTL_DATABASE_URL). Update connector
counts, test numbers, and planned→implemented status across docs. Convert 3
ASCII flow diagrams to Mermaid.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

examples/multi-issuer/docker-compose.yml

@@ -27,7 +27,7 @@ services:
     container_name: certctl-server-multi-issuer
     environment:
       # Database
-      DATABASE_URL: postgres://certctl:${DB_PASSWORD:-certctl-dev-password}@postgres:5432/certctl?sslmode=disable
+      CERTCTL_DATABASE_URL: postgres://certctl:${DB_PASSWORD:-certctl-dev-password}@postgres:5432/certctl?sslmode=disable
 
       # Server settings
       CERTCTL_SERVER_PORT: 8443
@@ -64,7 +64,7 @@ services:
     networks:
       - certctl-network
     healthcheck:
-      test: ['CMD-SHELL', 'curl -sf http://localhost:8443/api/v1/health || exit 1']
+      test: ['CMD-SHELL', 'curl -sf http://localhost:8443/health || exit 1']
       interval: 10s
       timeout: 5s
       retries: 3