refactor: Split Keymaster API routes

[macterra]

Summary

• split the Keymaster v1 API handlers out of keymaster-api.ts into public, core, identity, credential, and content routers
• move the admin API key middleware into keymaster-admin.ts and share dependencies through router options
• update Swagger source discovery to read the new Keymaster router files in route order
• document the Keymaster route-split ordering rule in AGENTS.md

Validation

• npx tsc -p services/keymaster/server/tsconfig.json --noEmit
• route inventory check: old 155 new 155, order unchanged
• node --experimental-vm-modules node_modules/.bin/jest tests/keymaster/client.test.ts --runInBand
• npm run generate-openapi with no generated docs content change