Add collapsible primary UI sections (ticket 035)

Log viewer (FilterBar+LogTimeline+LogPreview), Params, Metrics, and
Dashboards can each be collapsed/expanded via a toggle next to their
existing help icon. Collapsed state persists per-section in
localStorage (ottyl.collapsedSections) and content is hidden with the
`hidden` attribute rather than unmounted, so in-progress form state
(a half-filled Metrics/Params form, in-progress Dashboards panel
edits) survives a collapse/expand cycle.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/src/App.tsx

@@ -7,6 +7,7 @@ import { Params } from './components/Params'
 import { Metrics } from './components/Metrics'
 import { Dashboards } from './components/Dashboards'
 import { Alerts } from './components/Alerts'
+import { CollapseToggle, useSectionCollapsed } from './components/CollapsibleSection'
 import {
   fetchLogs,
   fetchParamDeclarations,
@@ -30,6 +31,7 @@ export default function App() {
   const [activePreset, setActivePreset] = useState<TimeRangePresetId | null>('all')
   const [filter, setFilter] = useState('')
   const [filterError, setFilterError] = useState<string | null>(null)
+  const [logViewerCollapsed, setLogViewerCollapsed] = useSectionCollapsed('log-viewer')
 
   // Read from inside the poll loop below without making it a dependency —
   // a rolling preset's own re-resolution (ticket 024) updates `range`, and
@@ -123,15 +125,24 @@ export default function App() {
       <div className="flex h-screen w-screen overflow-hidden">
         <NavMenu stats={stats} />
         <div className="flex min-w-0 flex-1 flex-col">
-          <FilterBar value={filter} onChange={setFilter} error={filterError} />
-          <LogTimeline
-            buckets={buckets}
-            range={range}
-            onSelectRange={handleManualRangeSelect}
-            activePreset={activePreset}
-            onSelectPreset={selectPreset}
+          <FilterBar
+            value={filter}
+            onChange={setFilter}
+            error={filterError}
+            collapseToggle={
+              <CollapseToggle collapsed={logViewerCollapsed} onToggle={() => setLogViewerCollapsed(!logViewerCollapsed)} />
+            }
           />
-          <LogPreview logs={logs} params={params} />
+          <div className="flex min-h-0 flex-1 flex-col" hidden={logViewerCollapsed}>
+            <LogTimeline
+              buckets={buckets}
+              range={range}
+              onSelectRange={handleManualRangeSelect}
+              activePreset={activePreset}
+              onSelectPreset={selectPreset}
+            />
+            <LogPreview logs={logs} params={params} />
+          </div>
           <Params params={params} onDeclared={loadParams} />
           <Metrics range={range} />
           <Dashboards range={range} />