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/components/Params.tsx

@@ -1,5 +1,6 @@
 import { useState } from 'react'
 import { ApiError, declareParam, type ParamDeclaration } from '../lib/api'
+import { CollapseToggle, useSectionCollapsed } from './CollapsibleSection'
 import { HelpIcon } from './HelpIcon'
 
 const EMPTY_KIND: ParamDeclaration['kind'] = 'string'
@@ -11,6 +12,7 @@ export function Params({ params, onDeclared }: { params: ParamDeclaration[]; onD
   const [kind, setKind] = useState<ParamDeclaration['kind']>(EMPTY_KIND)
   const [submitError, setSubmitError] = useState<string | null>(null)
   const [submitting, setSubmitting] = useState(false)
+  const [collapsed, setCollapsed] = useSectionCollapsed('params')
 
   async function handleSubmit(e: React.FormEvent) {
     e.preventDefault()
@@ -35,8 +37,9 @@ export function Params({ params, onDeclared }: { params: ParamDeclaration[]; onD
       <div className="mb-2 flex items-center gap-1.5 text-xs text-text-subtle">
         Params
         <HelpIcon sectionId="parameters" label="Help: Params" />
+        <CollapseToggle collapsed={collapsed} onToggle={() => setCollapsed(!collapsed)} />
       </div>
-      <div className="flex gap-4">
+      <div className="flex gap-4" hidden={collapsed}>
         <form onSubmit={handleSubmit} className="w-80 shrink-0 space-y-2">
           <div>
             <label className="mb-1 block text-xs text-text-subtle">Name</label>