feat(dashboard): improve real-time updates and scroll behavior

Major UX improvements to conversation display and state management.

Scroll behavior (SessionCard.js):
- Replace scroll-position tracking with wheel-event intent detection
- Accumulate scroll-up distance before disabling sticky mode (50px threshold)
- Re-enable sticky on scroll-down when near bottom (100px threshold)
- Always scroll to bottom on first load or user's own message submission
- Use requestAnimationFrame for smooth scroll positioning

Optimistic updates (App.js):
- Immediately show user messages before API confirmation
- Remove optimistic message on send failure
- Eliminates perceived latency when sending responses

Error tracking integration (App.js):
- Wire up trackError/clearErrorCount for API operations
- Track: state fetch, conversation fetch, respond, dismiss, SSE init/parse
- Clear error counts on successful operations
- Clear SSE event cache on reconnect to force refresh

Conversation management (App.js):
- Use mtime_ns (preferred) or last_event_at for change detection
- Clean up conversation cache when sessions are dismissed
- Add modalSessionRef for stable reference across renders

Message stability (ChatMessages.js):
- Prefer server-assigned message IDs for React keys
- Fallback to role+timestamp+index for legacy messages

Input UX (SimpleInput.js):
- Auto-refocus textarea after successful submission
- Use setTimeout to ensure React has re-rendered first

Sorting simplification (status.js):
- Remove status-based group/session reordering
- Return groups in API order (server handles sorting)

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

dashboard/components/SimpleInput.js

@@ -1,4 +1,4 @@
-import { html, useState } from '../lib/preact.js';
+import { html, useState, useRef } from '../lib/preact.js';
 import { getStatusMeta } from '../utils/status.js';
 
 export function SimpleInput({ sessionId, status, onRespond }) {
@@ -6,6 +6,7 @@ export function SimpleInput({ sessionId, status, onRespond }) {
   const [focused, setFocused] = useState(false);
   const [sending, setSending] = useState(false);
   const [error, setError] = useState(null);
+  const textareaRef = useRef(null);
   const meta = getStatusMeta(status);
 
   const handleSubmit = async (e) => {
@@ -22,6 +23,11 @@ export function SimpleInput({ sessionId, status, onRespond }) {
         console.error('SimpleInput send error:', err);
       } finally {
         setSending(false);
+        // Refocus the textarea after submission
+        // Use setTimeout to ensure React has re-rendered with disabled=false
+        setTimeout(() => {
+          textareaRef.current?.focus();
+        }, 0);
       }
     }
   };
@@ -35,6 +41,7 @@ export function SimpleInput({ sessionId, status, onRespond }) {
       `}
       <div class="flex items-end gap-2.5">
       <textarea
+        ref=${textareaRef}
         value=${text}
         onInput=${(e) => {
           setText(e.target.value);