FEAT: improve conversation history loading for long sessions (#371)

* feat: add "Load all messages" button for long conversations

Scrolling up through long conversations requires many "load more" cycles.
This adds a "Load all messages" floating button that fetches the entire
conversation history in one shot.

- Floating overlay pill appears after each batch finishes loading, persists 2s
- Shows loading spinner while fetching all messages
- Shows green "All messages loaded" confirmation for 1s before disappearing
- Preserves scroll position when bulk-loading (no viewport jump)
- Ref-based guards prevent scroll handler from re-fetching after load-all
- Performance warning shown; "Scroll to bottom" resets visible cap
- Clean state reset on session switch
- i18n keys for en and zh-CN

Note: default page size (20) and visible cap (100) are unchanged.
These could be increased in a follow-up or made configurable via settings.

* re-implement load-all feature for new TS architecture

src/components/chat/view/ChatInterface.tsx

@@ -96,11 +96,17 @@ function ChatInterface({
     visibleMessageCount,
     visibleMessages,
     loadEarlierMessages,
+    loadAllMessages,
+    allMessagesLoaded,
+    isLoadingAllMessages,
+    loadAllJustFinished,
+    showLoadAllOverlay,
     claudeStatus,
     setClaudeStatus,
     createDiff,
     scrollContainerRef,
     scrollToBottom,
+    scrollToBottomAndReset,
     handleScroll,
   } = useChatSessionState({
     selectedProject,
@@ -297,6 +303,11 @@ function ChatInterface({
           visibleMessageCount={visibleMessageCount}
           visibleMessages={visibleMessages}
           loadEarlierMessages={loadEarlierMessages}
+          loadAllMessages={loadAllMessages}
+          allMessagesLoaded={allMessagesLoaded}
+          isLoadingAllMessages={isLoadingAllMessages}
+          loadAllJustFinished={loadAllJustFinished}
+          showLoadAllOverlay={showLoadAllOverlay}
           createDiff={createDiff}
           onFileOpen={onFileOpen}
           onShowSettings={onShowSettings}
@@ -327,7 +338,7 @@ function ChatInterface({
           onClearInput={handleClearInput}
           isUserScrolledUp={isUserScrolledUp}
           hasMessages={chatMessages.length > 0}
-          onScrollToBottom={scrollToBottom}
+          onScrollToBottom={scrollToBottomAndReset}
           onSubmit={handleSubmit}
           isDragActive={isDragActive}
           attachedImages={attachedImages}