Add contextual "?" help icons linking into Docs (ticket 021)

New HelpIcon component + a DocsNavProvider context (webapp/src/lib/docsNav.tsx)
let any component request "open Docs to section X", bumping a nonce each
time so a repeat click re-triggers even if Docs is already open to that
section. NavMenu forwards that request into DocsPanel as a `target` prop,
which expands the right accordion section, scrolls it into view, and
flashes it (a brief accent-tinted background/border, settling back after
1.2s) — verified visually with a live server + Playwright. Opening Docs via
the plain NavMenu button explicitly clears any pending target, so that path
is unchanged: no forced section, no flash.

Added a "?" icon to FilterBar, LogTimeline, LogPreview, Metrics, Dashboards,
and NavMenu's own Settings/Presets panels, plus new Docs sections for
Timeline, Log preview, Settings, and Presets (previously undocumented).

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

webapp/src/App.tsx

@@ -6,6 +6,7 @@ import { LogPreview } from './components/LogPreview'
 import { Metrics } from './components/Metrics'
 import { Dashboards } from './components/Dashboards'
 import { fetchLogs, fetchStats, fetchTimeline, type LogEntry, type Stats, type TimelineBucket } from './lib/api'
+import { DocsNavProvider } from './lib/docsNav'
 
 const POLL_MS = 2000
 
@@ -49,15 +50,17 @@ export default function App() {
   }, [range, filter])
 
   return (
-    <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={setRange} />
-        <LogPreview logs={logs} />
-        <Metrics range={range} />
-        <Dashboards range={range} />
+    <DocsNavProvider>
+      <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={setRange} />
+          <LogPreview logs={logs} />
+          <Metrics range={range} />
+          <Dashboards range={range} />
+        </div>
       </div>
-    </div>
+    </DocsNavProvider>
   )
 }