Fix Prometheus range query encoding

[Hanabi9248]

Steps to reproduce

Configure a Prometheus monitor query containing addition, such as sum(up) + 1. The range-query helper encodes only label selectors inside braces, leaving the + unescaped. After URL parameter decoding, Prometheus receives sum(up) 1.

Design of the fix

Encode the complete expression once when building the range query. This preserves operators outside label selectors while keeping quoted characters inside them intact.

Automated tests and validation

The regression checks the decoded expression and the start, end, and step parameters using sum(up{job="a&b#50%",name=~".+"}) + 1. It fails before the change.

• All 42 helper, query-client, and Prometheus-monitor tests pass.
• Core ESLint and license checks pass.
• The full core suite has 356 passing tests and one failure on Windows: CaliperEngine / should stop the benchmark if the benchmark has been started. The unmodified baseline has the same failure (355 passing), caused by its shell command.

Tested with Node 24.19.0. Fabric/Docker integration tests were not run. No documentation or public API changes.