feat(ui): sync filter state to URL query params for deep-linking

[comnam90]

Summary

The provider filter and service multi-select filters in layouts/index.html are purely in-memory state. Applying filters then sharing the URL or using the browser back button loses all filter context. URL state sync would enable deep-linking, bookmarking, and sharing a filtered view.

Desired behaviour

• Selecting provider filter → ?provider=Azure appended to URL
• Selecting one or more services → ?services=vdc_vault,vdc_m365 appended
• On page load, read query params and pre-apply filters before first renderMap() call
• Clearing all filters removes params from URL (clean URL)
• Browser back/forward navigates filter history

Implementation notes

• Use history.replaceState() (not pushState) on filter change to avoid polluting history on every keystroke
• Parse params on load with new URLSearchParams(location.search)
• No router library needed — the page is a single-file SPA
• Search input state should not be synced (transient UI, no value in persisting)

Acceptance criteria

• Provider filter reflected as ?provider=<value> in URL (omitted when all)
• Service filters reflected as ?services=<comma-separated-ids> in URL (omitted when none)
• Refreshing the page restores the filter state
• Sharing the URL to another browser produces the same filtered map view
• npm run test:ui passes (add a test that verifies URL updates on filter change)