fix: correct stale counts across all docs (tables 19→21, MCP tools 76→78, tests 860→900+)

V2 audit found 3 critical number mismatches propagated across 8 files:
- Table count was 19 everywhere but actual migrations create 21 tables
- MCP tool count was 76 but tools.go registers 78 (M21/M22 additions)
- README MCP breakdown claimed 83 tools with math summing to 90
- architecture.md still had stale 860+ test count
- features.md OpenAPI claim said 93 ops but spec has 78
- mcp.md tool-per-domain table had wrong counts in 10 of 16 rows
- Added 3 network_scan_targets to seed_demo.sql for demo completeness
- Added curl examples to Agent Groups section in features.md

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

docs/concepts.md

@@ -186,7 +186,7 @@ The CLI supports both table and JSON output formats (`--format table` or `--form
 
 ### MCP Server (AI Integration)
 
-certctl includes an MCP (Model Context Protocol) server that exposes all 76 API endpoints as MCP tools. This enables AI assistants like Claude, Cursor, and other MCP-compatible tools to interact with your certificate infrastructure using natural language — "show me all expiring certificates," "revoke the VPN cert," or "what agents are offline?"
+certctl includes an MCP (Model Context Protocol) server that exposes all 78 API endpoints as MCP tools. This enables AI assistants like Claude, Cursor, and other MCP-compatible tools to interact with your certificate infrastructure using natural language — "show me all expiring certificates," "revoke the VPN cert," or "what agents are offline?"
 
 The MCP server is a separate binary (`cmd/mcp-server/`) that communicates via stdio transport and acts as a stateless HTTP proxy to the certctl REST API. It requires no additional infrastructure — just point it at your certctl server URL and API key.