Add URL query-parameter filtering for dashboards

[TanayBensuYurtturk]

Dashboards can now be filtered straight from the URL, so a filtered view is a shareable link (e.g. ?region=Europe&date_range=last_30_days). Filter values sync both ways with the URL, and select/date/number values from the URL are validated so anything invalid or injected is ignored and falls back to the default.

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 1
frontend/src/components/DashboardView.tsx:149
**Local state shadows URL changes**

When a viewer edits a filter and then navigates to the same dashboard with different query parameters, the non-null local `filters` state continues to override the recomputed `baseFilters`, causing the controls and widget queries to use values that disagree with the visible URL.

_{Reviews (1): Last reviewed commit: "Harden URL filter parsing and use repeat..." | Re-trigger Greptile}

[greptile-apps]

Prompt To Fix All With AI

### Issue 1
frontend/src/components/DashboardView.tsx:266
**Concurrent URL writes drop filters**

When two filter controls invoke this handler before the first URL update causes a rerender, both calls clone the same render-time search parameters. The second write drops the first changed parameter while local state retains both filters, so copying or reloading the URL loses an active filter.

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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (2): Last reviewed commit: "Re-apply URL filters on external navigat..." | Re-trigger Greptile}

[greptile-apps]

Prompt To Fix All With AI

### Issue 1
frontend/src/components/DashboardView.tsx:211
**Persistent marker ignores navigation**

When an external navigation returns to the same query string as the most recent local URL write while local filter state differs, this persistent marker classifies it as the original self-write and skips clearing `filters`, causing the controls and widget queries to remain out of sync with the navigated URL.

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For each issue above, determine whether it is valid and should be fixed. If so, fix it directly.

_{Reviews (3): Last reviewed commit: "Sync dashboard filters with the URL via ..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (4): Last reviewed commit: "Keep the self-write marker in sync so na..." | Re-trigger Greptile}

[greptile-apps]

_{Reviews (5): Last reviewed commit: "Keep the self-write marker in sync so na..." | Re-trigger Greptile}