chore: Remove OpenCorporates integration (requires paid plan for commercial use)

Keep only the genuinely free APIs:
- FCA Register (free with registration)
- SRA Register (free public API)
- GitHub (free tier sufficient)
- ORCID (free public API)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/RealCV.Web/appsettings.json

@@ -25,9 +25,6 @@
   "GitHub": {
     "PersonalAccessToken": ""
   },
-  "OpenCorporates": {
-    "ApiToken": ""
-  },
   "Serilog": {
     "MinimumLevel": {
       "Default": "Information",