Allow separate OpenSpeedTest save and results URLs

[Jason-Morcos]

Problem

The native OpenSpeedTest template assumes that result submissions and the Network Optimizer results page share one origin derived from SAVE_DATA_URL. Reverse-proxy deployments can legitimately serve the test UI on one host, submit results through a same-origin API route there, and show saved results on the Network Optimizer host.

Today those deployments have to rewrite the installed template after every update.

Fix

• add optional OPENSPEEDTEST_SAVE_DATA_URL and OPENSPEEDTEST_CLIENT_RESULTS_URL settings
• preserve the current derived URLs when neither setting is present
• accept only absolute HTTP(S) URLs or root-relative paths
• JSON-encode generated JavaScript values rather than interpolating raw strings
• document the two settings for native macOS installs

Validation

• tests cover independent routes, unchanged defaults, and rejection of unsafe URL shapes
• focused tests: 5 passed
• full Release NetworkOptimizer.Web.Tests: 1,285 passed

No deployed OpenSpeedTest files or proxy routes were changed while validating this fix.