feat: massive chat reliability + UX pass (web/desktop/mobile/vscode) (#593)

## Added Features
- Add VS Code save-as-image flow for assistant messages via webview bridge + native save dialog.
- Add hourly desktop update checks after startup.
- Add new tool output display mode: `Changes` (auto-expand edit/write/patch only; keep activity expanded; mode guidance text).
- Add GitHub PR attachment flow in chat input with PR picker + attached PR chip/details.
- Add mobile overlay presentation for GitHub Issue and PR pickers (shared with desktop picker content).

## Fixes
- Save-gate project icon updates until explicit Save; allow icon removal with same save-gated behavior.
- Restore clickable chat action buttons in sticky header mode (desktop + Firefox hit-target issue).
- Clamp sticky user messages to bounded chat height and allow internal scrolling.
- Prevent drawer context crash during iPad/tablet orientation switching.
- Improve text-selection action menu placement on narrow screens.
- Move assistant message time into clock tooltip; keep duration display clean.
- Hide `Link GitHub Issue` row in VS Code chat input area (GitHub flow is not yet ready there).
- Remove laggy close animation in text-selection popover; keep open motion/positioning behavior.
- Fetch branches when picker opens and cache empty; show loading state instead of false “No branches found”.
- Fix share-image export metadata rendering (theme background resolution, timestamp rendering, footer alignment).
- Scope MCP services status/toggles to active directory to avoid cross-project leakage.
- Improve long user-message clamp behavior (40% cap variant, hidden scrollbar, scroll shadows, expansion detection).
- Fix desktop `Check for Updates` menu handler; prevent duplicate checks; show clear success/error toasts.
- Stabilize long user-message scrolling behavior (follow-up hardening).
- Avoid premature web update failure on slower servers.
- Restore user message image previews + fullscreen gallery navigation payload.
- Repair desktop chat drag-and-drop image attachments when native drop coords are missing.
- Move GitHub issue linking entry into Add attachment menu.
- Align header context usage percentage visuals with context panel.
- Align `@` file search with active project in all runtimes.
- Route `@` file discovery through OpenCode SDK `find.files`; remove legacy `/api/fs/search` reliance.
- Make chat `@` mention behavior consistent with files-style behavior.
- Keep status-row todos in stable order after status changes; add compact status icons; replace noisy priority labels.

## Refactors / UX Consistency
- Simplify chat attachment model and remove project file picker path.
- Keep composer focused on `@` mention file flow.
- Use direct `Attach files` action in VS Code instead of attachment dropdown path.
- Unify issue/PR picker behavior between desktop and mobile overlays.

packages/ui/src/components/chat/ChatContainer.tsx

@@ -327,6 +327,33 @@ export const ChatContainer: React.FC = () => {
         trimToViewportWindow,
     });
 
+    React.useLayoutEffect(() => {
+        const container = scrollRef.current;
+        if (!container) {
+            return;
+        }
+
+        const updateChatScrollHeight = () => {
+            container.style.setProperty('--chat-scroll-height', `${container.clientHeight}px`);
+        };
+
+        updateChatScrollHeight();
+
+        if (typeof ResizeObserver === 'undefined') {
+            window.addEventListener('resize', updateChatScrollHeight);
+            return () => {
+                window.removeEventListener('resize', updateChatScrollHeight);
+            };
+        }
+
+        const resizeObserver = new ResizeObserver(updateChatScrollHeight);
+        resizeObserver.observe(container);
+
+        return () => {
+            resizeObserver.disconnect();
+        };
+    }, [currentSessionId, isDesktopExpandedInput, scrollRef]);
+
     React.useEffect(() => {
         cancelTurnBackfill();
         if (!currentSessionId) {