feat: unified sessions — merge assistant chat into ai_sessions table

Add session_type ('guided'|'chat') and title columns to ai_sessions,
enabling both FlowPilot guided sessions and assistant chat sessions to
live in a single table. This is the foundation for a unified session
history and consistent UX across both interaction modes.

Backend:
- Migration 066: session_type + title columns
- unified_chat_service: chat sessions on ai_sessions with same AI/RAG
- POST /ai-sessions supports session_type='chat' creation
- POST /ai-sessions/{id}/chat for chat messages
- DELETE /ai-sessions/{id} for session deletion
- session_type filter on GET /ai-sessions

Frontend:
- AssistantChatPage rewired to aiSessionsApi (no more assistantChatApi)
- /assistant/:sessionId route for deep-linking
- Session history: type filter pills (All/Guided/Chat), type icons
- Dashboard: both types shown with correct routing and icons
- Fixed glass-border → border-default in dashboard components

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/SessionHistoryPage.tsx

@@ -27,6 +27,7 @@ export function SessionHistoryPage() {
   const aiSearchTimeout = useRef<ReturnType<typeof setTimeout> | undefined>(undefined)
   const [aiFilters, setAiFilters] = useState({
     q: '',
+    session_type: '',
     problem_domain: '',
     confidence_tier: '',
     date_from: '',
@@ -176,6 +177,7 @@ export function SessionHistoryPage() {
         const data = await aiSessionsApi.listSessions({
           limit: 50,
           q: aiFilters.q || undefined,
+          session_type: aiFilters.session_type || undefined,
           problem_domain: aiFilters.problem_domain || undefined,
           confidence_tier: aiFilters.confidence_tier || undefined,
           date_from: aiFilters.date_from || undefined,
@@ -267,7 +269,7 @@ export function SessionHistoryPage() {
     return labels[outcome] ?? outcome
   }
 
-  const hasAiFiltersActive = !!(aiSearchInput || aiFilters.q || aiFilters.problem_domain || aiFilters.confidence_tier || aiFilters.date_from || aiFilters.date_to)
+  const hasAiFiltersActive = !!(aiSearchInput || aiFilters.q || aiFilters.session_type || aiFilters.problem_domain || aiFilters.confidence_tier || aiFilters.date_from || aiFilters.date_to)
   const hasFlowFiltersActive = !!(filters.ticketNumber || filters.clientName || filters.treeName || filters.dateRange?.from)
 
   // Determine section visibility
@@ -314,7 +316,7 @@ export function SessionHistoryPage() {
       {/* FlowPilot Sessions Section */}
       {showAiSection && (
         <>
-          <h2 className="font-sans text-xs text-[0.625rem] uppercase tracking-[0.1em] text-muted-foreground mb-3">FlowPilot Sessions</h2>
+          <h2 className="font-sans text-xs text-[0.625rem] uppercase tracking-[0.1em] text-muted-foreground mb-3">AI Sessions</h2>
 
           {/* AI Session Filter Bar */}
           <div className="card-flat p-3 mb-4">
@@ -331,6 +333,24 @@ export function SessionHistoryPage() {
                 />
               </div>
 
+              {/* Session type pills */}
+              <div className="flex gap-1">
+                {(['', 'guided', 'chat'] as const).map((t) => (
+                  <button
+                    key={t}
+                    onClick={() => setAiFilters((f) => ({ ...f, session_type: t }))}
+                    className={cn(
+                      'rounded-full border px-3 py-1 text-xs font-sans transition-colors',
+                      aiFilters.session_type === t
+                        ? 'bg-accent-dim text-foreground border-primary/30'
+                        : 'bg-card text-muted-foreground border-border hover:text-foreground hover:border-[rgba(255,255,255,0.12)]'
+                    )}
+                  >
+                    {t === '' ? 'All' : t === 'guided' ? 'Guided' : 'Chat'}
+                  </button>
+                ))}
+              </div>
+
               {/* Problem domain dropdown */}
               <select
                 value={aiFilters.problem_domain}
@@ -393,7 +413,7 @@ export function SessionHistoryPage() {
                 <button
                   onClick={() => {
                     setAiSearchInput('')
-                    setAiFilters({ q: '', problem_domain: '', confidence_tier: '', date_from: '', date_to: '' })
+                    setAiFilters({ q: '', session_type: '', problem_domain: '', confidence_tier: '', date_from: '', date_to: '' })
                   }}
                   className="text-xs text-muted-foreground hover:text-foreground transition-colors"
                 >
@@ -415,7 +435,7 @@ export function SessionHistoryPage() {
                 <button
                   onClick={() => {
                     setAiSearchInput('')
-                    setAiFilters({ q: '', problem_domain: '', confidence_tier: '', date_from: '', date_to: '' })
+                    setAiFilters({ q: '', session_type: '', problem_domain: '', confidence_tier: '', date_from: '', date_to: '' })
                   }}
                   className="text-foreground hover:underline text-sm"
                 >