docs: comprehensive documentation audit — fix stale counts, V2/V3 matrix, connector status

- features.md: Fix Feature Matrix to correctly show all V2 Free features
  (F5/IIS/WinCertStore/JavaKeystore as Implemented, not Stub; Vault/DigiCert/
  Sectigo/GoogleCAS as V2 Free, not V3 Paid). Add missing shipped features
  (EST, verification, export, S/MIME, ARI, digest, Helm, onboarding). Update
  issuer count to 9, target count to 13.
- architecture.md: Fix F5/IIS from "interface only, implementation planned"
  to implemented. Add all 13 target connectors to built-in targets list.
- why-certctl.md: Add Sectigo and Google CAS to issuer list (7→9). Fix
  target count (10→13). Remove hardcoded endpoint/operation counts.
- connectors.md: Fix F5 BIG-IP TOC entry from "Interface Only" to
  "Implemented". Remove dead "Planned Issuers" TOC link.
- README.md: Remove competitor product names (CertKit, KeyTalk). Remove
  hardcoded dashboard page count. Remove hardcoded endpoint counts. Fix V4
  roadmap to remove already-shipped issuers (Sectigo, Google CAS).
- Remove hardcoded MCP tool counts (78/80) across 8 files (mcp.md,
  architecture.md, features.md, testing-guide.md, concepts.md, quickstart.md,
  demo-advanced.md, why-certctl.md). Replace with "REST API exposed via MCP"
  to avoid future drift.
- quickstart.md: Docker Compose environments table (from previous session).

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

docs/demo-advanced.md

@@ -981,7 +981,7 @@ export CERTCTL_API_KEY="test-key-123"
 
 ## Part 15: MCP Server for AI Integration (M18a)
 
-certctl exposes 78 MCP tools covering the REST API via the Model Context Protocol (MCP), enabling seamless integration with Claude, Cursor, and other AI assistants:
+certctl exposes the full REST API via the Model Context Protocol (MCP), enabling seamless integration with Claude, Cursor, and other AI assistants:
 
 ```bash
 # Build the MCP server