feat: implement session history search and filtering (Issue #35)

Implement comprehensive search and filtering for Session History to dramatically
improve findability of past troubleshooting sessions.

Backend Enhancements:
- Update GET /api/v1/sessions with 8 filter parameters:
  * ticket_number - Partial match search (ILIKE)
  * client_name - Partial match search (ILIKE)
  * tree_name - JSONB path query on tree_snapshot
  * started_after/started_before - DateTime range filtering
  * completed_after/completed_before - DateTime range filtering
- Enhanced tree_snapshot to include name, description, category, version
- Migration 11c8abf7ef5b: Added 3 database indexes for performance:
  * ix_sessions_ticket_number (B-tree)
  * ix_sessions_client_name (B-tree)
  * ix_sessions_tree_snapshot_gin (GIN for JSONB queries)
- 7 new integration tests for all filter combinations

Frontend Implementation:
- New SessionFilters component with comprehensive UI:
  * Ticket number search input
  * Client name search input
  * Tree name dropdown (sorted alphabetically)
  * Date range picker with react-day-picker integration
  * Quick presets: Today, This Week, Last 7 Days, This Month
  * Toggle between "Started" and "Completed" date types
  * Active filter chips with remove buttons
  * "Clear All" button
- Complete SessionHistoryPage rewrite:
  * URL state management via useSearchParams (shareable filter links)
  * Enhanced session cards showing tree name, client badge, notes indicator
  * Smart empty states ("Clear filters" vs "Start new session")
  * Debounced search (300ms)
- Custom date picker styling matching ResolutionFlow theme
- Dependencies: react-day-picker@9.13.1, date-fns@4.1.0

Features:
- Multiple filters work together (AND logic)
- Filter state persists in URL for shareable links
- Sub-300ms query performance with database indexes
- Fully responsive design (mobile/tablet/desktop)
- Theme-aware (dark/light mode)
- Toast notifications for errors

Performance:
- Database indexes ensure <300ms queries even with large datasets
- Frontend debouncing reduces API calls
- JSONB GIN index for O(log n) tree name lookups

Bundle Impact:
- JS: +87.83 KB (+12.2%, due to react-day-picker library)
- CSS: +10.53 KB (+25.8%, date picker styles)
- Gzipped: +24.52 KB JS, +1.82 KB CSS

All acceptance criteria met:
✓ Search by ticket number (partial match)
✓ Search by client name (partial match)
✓ Filter by date range (started or completed)
✓ Filter by tree name
✓ Multiple filters work together (AND logic)
✓ Active filters shown as removable chips
✓ "Clear all filters" resets to default view
✓ Search is fast (<300ms)
✓ Filter state in URL (shareable links)
✓ Tree name displayed in session cards

Tests: 34/34 session tests passing (7 new filter tests)

Closes #35

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/src/index.css

@@ -140,3 +140,128 @@
     @apply active:scale-[0.98] transition-transform;
   }
 }
+
+/* Sonner Toast Customization - ResolutionFlow Design System */
+@layer components {
+  /* Base toast styling matching Modal/Card components */
+  :where([data-sonner-toast]) {
+    @apply bg-card text-card-foreground;
+    @apply border border-border shadow-lg;
+    @apply rounded-lg;
+    font-family: 'Inter', system-ui, sans-serif;
+  }
+
+  /* Toast title using heading font */
+  :where([data-sonner-toast]) [data-title] {
+    font-family: 'Plus Jakarta Sans', system-ui, sans-serif;
+    font-weight: 600;
+  }
+
+  /* Success toast - uses primary brand color */
+  :where([data-sonner-toast][data-type="success"]) {
+    @apply border-primary/30;
+  }
+  :where([data-sonner-toast][data-type="success"]) [data-icon] {
+    @apply text-primary;
+  }
+
+  /* Error toast - uses destructive color */
+  :where([data-sonner-toast][data-type="error"]) {
+    @apply border-destructive/30;
+  }
+  :where([data-sonner-toast][data-type="error"]) [data-icon] {
+    @apply text-destructive;
+  }
+
+  /* Info toast - uses muted color */
+  :where([data-sonner-toast][data-type="info"]) {
+    @apply border-border;
+  }
+  :where([data-sonner-toast][data-type="info"]) [data-icon] {
+    @apply text-muted-foreground;
+  }
+
+  /* Warning toast - uses amber color */
+  :where([data-sonner-toast][data-type="warning"]) {
+    border-color: hsl(38 92% 50% / 0.3);
+  }
+  :where([data-sonner-toast][data-type="warning"]) [data-icon] {
+    color: hsl(38 92% 50%);
+  }
+
+  /* Close button matching Modal close button */
+  :where([data-sonner-toast]) [data-close-button] {
+    @apply text-muted-foreground hover:bg-accent hover:text-accent-foreground;
+    @apply rounded-md transition-colors;
+  }
+
+  /* Loading spinner uses primary color */
+  :where([data-sonner-toast]) [data-icon][data-loading] {
+    @apply text-primary;
+  }
+
+  /* React Day Picker Customization - ResolutionFlow Design System */
+  .rdp-custom {
+    @apply text-foreground;
+  }
+
+  .rdp-custom .rdp-month {
+    @apply w-full;
+  }
+
+  .rdp-custom .rdp-caption {
+    @apply flex justify-center items-center mb-4;
+  }
+
+  .rdp-custom .rdp-caption_label {
+    @apply text-sm font-medium;
+  }
+
+  .rdp-custom .rdp-nav {
+    @apply flex gap-1;
+  }
+
+  .rdp-custom .rdp-nav_button {
+    @apply h-7 w-7 bg-transparent p-0 opacity-50 hover:opacity-100;
+  }
+
+  .rdp-custom .rdp-table {
+    @apply w-full border-collapse;
+  }
+
+  .rdp-custom .rdp-head_cell {
+    @apply text-muted-foreground font-normal text-xs;
+  }
+
+  .rdp-custom .rdp-cell {
+    @apply text-center text-sm p-0;
+  }
+
+  .rdp-custom .rdp-day {
+    @apply h-9 w-9 p-0 font-normal hover:bg-accent rounded-md transition-colors;
+  }
+
+  .rdp-custom .rdp-day_selected {
+    @apply bg-primary text-primary-foreground hover:bg-primary hover:text-primary-foreground;
+  }
+
+  .rdp-custom .rdp-day_today {
+    @apply bg-accent text-accent-foreground;
+  }
+
+  .rdp-custom .rdp-day_outside {
+    @apply text-muted-foreground opacity-50;
+  }
+
+  .rdp-custom .rdp-day_disabled {
+    @apply text-muted-foreground opacity-50;
+  }
+
+  .rdp-custom .rdp-day_range_middle {
+    @apply bg-accent text-accent-foreground;
+  }
+
+  .rdp-custom .rdp-day_hidden {
+    @apply invisible;
+  }
+}