Add Grafana-style time range presets: All, 5m, 15m, 1h, 24h (ticket 024)

LogTimeline gets a preset button row (All + four relative windows)
next to the existing drag-select interaction. App.tsx lifts the
active preset alongside `range`; a relative preset re-resolves to a
fresh {startMs, endMs} on the same 2s cadence the app already polls
on, so it visibly rolls forward rather than freezing at selection
time. Dragging on the timeline (or picking a different preset)
overrides back to a fixed range, matching today's drag behavior.

The rolling re-resolution reads/writes `range` via a ref inside the
poll loop instead of depending on `range` directly, since a naive
`setRange` inside an effect keyed on `range` would restart the effect
(and its interval) every tick — turning "poll every 2s" into "poll as
fast as React can re-render." Verified live: exactly 3 /api/stats
calls over ~6.2s with a rolling preset active, and console/network
free of errors.

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

webapp/src/components/LogTimeline.tsx

@@ -7,14 +7,42 @@ export interface TimeRange {
   endMs: number
 }
 
+/// A Grafana-style relative time-range preset (ticket 024). `'all'` clears
+/// the range (today's implicit default); the rest resolve to a window
+/// ending "now" at the moment they're (re-)computed — see `computePresetRange`.
+export type TimeRangePresetId = 'all' | '5m' | '15m' | '1h' | '24h'
+
+export const TIME_RANGE_PRESETS: { id: TimeRangePresetId; label: string; ms: number | null }[] = [
+  { id: 'all', label: 'All', ms: null },
+  { id: '5m', label: '5m', ms: 5 * 60 * 1000 },
+  { id: '15m', label: '15m', ms: 15 * 60 * 1000 },
+  { id: '1h', label: '1h', ms: 60 * 60 * 1000 },
+  { id: '24h', label: '24h', ms: 24 * 60 * 60 * 1000 },
+]
+
+/// Resolves a preset to a concrete `{startMs, endMs}` window as of *now* —
+/// callers re-invoke this on the same cadence they already poll on to keep a
+/// rolling preset's window moving with time (see `App.tsx`), rather than
+/// freezing it at selection time.
+export function computePresetRange(id: TimeRangePresetId): TimeRange | null {
+  const preset = TIME_RANGE_PRESETS.find((p) => p.id === id)
+  if (!preset || preset.ms == null) return null
+  const now = Date.now()
+  return { startMs: now - preset.ms, endMs: now }
+}
+
 export function LogTimeline({
   buckets,
   range,
   onSelectRange,
+  activePreset,
+  onSelectPreset,
 }: {
   buckets: TimelineBucket[]
   range: TimeRange | null
   onSelectRange: (range: TimeRange | null) => void
+  activePreset: TimeRangePresetId | null
+  onSelectPreset: (id: TimeRangePresetId) => void
 }) {
   const containerRef = useRef<HTMLDivElement>(null)
   const [dragStartX, setDragStartX] = useState<number | null>(null)
@@ -64,11 +92,32 @@ export function LogTimeline({
           Timeline
           <HelpIcon sectionId="timeline" label="Help: Timeline" />
         </span>
-        {range && (
-          <button className="underline hover:text-text-secondary" onClick={() => onSelectRange(null)}>
-            Clear selection
-          </button>
-        )}
+        <div className="flex items-center gap-1.5">
+          <div className="flex items-center gap-1">
+            {TIME_RANGE_PRESETS.map((preset) => (
+              <button
+                key={preset.id}
+                type="button"
+                onClick={() => onSelectPreset(preset.id)}
+                className={`rounded border px-1.5 py-0.5 text-[11px] ${
+                  activePreset === preset.id
+                    ? 'border-accent bg-accent/10 text-accent-text'
+                    : 'border-border-soft text-text-muted hover:bg-surface-2'
+                }`}
+              >
+                {preset.label}
+              </button>
+            ))}
+          </div>
+          {/* A dragged (custom, non-preset) selection — presets already show
+              their own active state above, so this only appears for the
+              "fixed range from a drag" case. */}
+          {range && activePreset === null && (
+            <button className="underline hover:text-text-secondary" onClick={() => onSelectPreset('all')}>
+              Clear selection
+            </button>
+          )}
+        </div>
       </div>
       <div
         ref={containerRef}