feat: unified global search & filter system with Cmd-K navigation

Replace per-page filtering with a single GlobalFilterProvider (time range +
status) consumed by a redesigned TopBar across all pages. Lift CommandPalette
to App level so Cmd-K works globally with filtered results that navigate to
exchanges, routes, agents, and applications. Sidebar auto-reveals and selects
the target entry on Cmd-K navigation via location state.

- Extract shared time preset utilities (computePresetRange, DEFAULT_PRESETS)
- Add GlobalFilterProvider (time range + status) and CommandPaletteProvider
- Add TimeRangeDropdown primitive with Popover preset list
- Redesign TopBar: breadcrumb | time dropdown | status pills | search | env
- Add application category to Cmd-K search
- Remove FilterBar and local DateRangePicker from Dashboard/Metrics pages
- Filter AgentHealth EventFeed by global time range
- Remove shift/onSearchClick props from TopBar

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/pages/Admin/Admin.tsx

@@ -10,7 +10,7 @@ export function Admin() {
       <TopBar
         breadcrumb={[{ label: 'Admin' }]}
         environment="PRODUCTION"
-        shift="Day (06:00-18:00)"
+
         user={{ name: 'hendrik' }}
       />
       <EmptyState