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/main.tsx

@@ -2,6 +2,8 @@ import { StrictMode } from 'react'
 import { createRoot } from 'react-dom/client'
 import { BrowserRouter } from 'react-router-dom'
 import { ThemeProvider } from './design-system/providers/ThemeProvider'
+import { GlobalFilterProvider } from './design-system/providers/GlobalFilterProvider'
+import { CommandPaletteProvider } from './design-system/providers/CommandPaletteProvider'
 import App from './App'
 import './index.css'
 
@@ -9,7 +11,11 @@ createRoot(document.getElementById('root')!).render(
   <StrictMode>
     <BrowserRouter>
       <ThemeProvider>
-        <App />
+        <GlobalFilterProvider>
+          <CommandPaletteProvider>
+            <App />
+          </CommandPaletteProvider>
+        </GlobalFilterProvider>
       </ThemeProvider>
     </BrowserRouter>
   </StrictMode>,