feat(timeline): add live filter, actor chips, group headers, copy button, source toggle, count badge

- Live search/filter bar: filters events by keyword across event, actor, source_excerpt, date
- Actor filter chips: click to filter by actor, multi-select, teal active state
- Year/month group headers when sorted chronologically (── 2023 ──, Mar 2024 ──)
- Per-event copy button (hover-revealed 📋): copies "date · actor · event" to clipboard
- "Hide/show sources" toggle: collapses all source excerpts without re-rendering
- Count badge: "23 events · 3 actors · 2022–2025" above the list
- applyTimelineFilters() unifies sort + actor + text filters in one re-render pass
- CSV export now includes end_date column
- Reset all filter state on each new run

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/deep-research.php

@@ -65,8 +65,9 @@ try {
     if (mb_strlen($advocateRole, 'UTF-8') > 200) {
         throw new DbnToolsHttpException('advocate_role is too long.', 422, 'advocate_role_too_long');
     }
-    $priorContext = is_array($input['prior_context'] ?? null) ? $input['prior_context'] : null;
-    $branchNotes  = mb_substr(trim((string)($input['branch_notes'] ?? '')), 0, 1000, 'UTF-8');
+    $priorContext        = is_array($input['prior_context'] ?? null) ? $input['prior_context'] : null;
+    $branchNotes        = mb_substr(trim((string)($input['branch_notes'] ?? '')), 0, 1000, 'UTF-8');
+    $subQsOverride      = is_array($input['sub_questions_override'] ?? null) ? $input['sub_questions_override'] : [];
 
     if (mb_strlen($seedQuery, 'UTF-8') > 4000) {
         throw new DbnToolsHttpException('Query is too long.', 422, 'query_too_long');
@@ -125,7 +126,8 @@ try {
         $emit,
         $advocateRole,
         $priorContext,
-        $branchNotes
+        $branchNotes,
+        $subQsOverride
     );
 
     $result['ok'] = true;