fix(web): prevent env editor draft crashes

[GatewayJ]

Summary

• keep agent profile draft comparison tolerant of incomplete environment variable rows
• preserve strict env and JSON validation for save payloads
• add a regression test for editing an env row with a missing key

Validation

• pnpm --dir web/app test -- tests/models/agents.test.ts
• pnpm --dir web/app typecheck
• pnpm --dir web/app lint
• pnpm --dir web/app format:check
• make build-web

Impact

Prevents the Agent profile advanced environment variable editor from crashing while users are still typing a new row.