feat(web): slim the list filters and hide them when empty

At current scale the date-range pickers are dead weight (UX review C1/C2):

- Drop the From/To date inputs from the filter bar; keep the Channel field and
  the "Summarized only" toggle. (Filter still parses from/to for hand-built
  URLs and apply() compatibility — only the UI is removed.)
- Hide the filter bar entirely on a genuinely empty account (no rows AND no
  active filter) so the connect CTA stands alone; a filter that matches nothing
  still shows the bar so it can be cleared.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/web/views.templ

@@ -107,7 +107,9 @@ templ flashBanner(code string) {
 templ ListPage(b listBuckets, f Filter, stats PipelineStats, flash string, hasConnected bool) {
 	@Layout("Tapir — Summaries") {
 		@flashBanner(flash)
-		@filterForm(f)
+		if !b.empty() || f.active() {
+			@filterForm(f)
+		}
 		if stats.RateLimited > 0 || stats.Pending > 0 || stats.NoText > 0 {
 			@pipelineBar(stats)
 		}
@@ -152,8 +154,6 @@ templ filterForm(f Filter) {
 		hx-indicator="#filter-indicator"
 	>
 		<label>Channel <input type="text" name="channel" value={ f.Channel } placeholder="any"/></label>
-		<label>From <input type="date" name="from" value={ f.From }/></label>
-		<label>To <input type="date" name="to" value={ f.To }/></label>
 		<label class="filter-check">
 			<input type="checkbox" name="summarized" value="1" if f.OnlySummarized { checked }/>
 			Summarized only