fix: mobile CJK input, terminal flicker, and layout overflow

Terminal flicker:
- Skip buffer-recovered/clear-terminal events during active buffer load
  to prevent competing clear+rewrite cycles (app.js)
- Move viewport+scrollback clear inside dimension-change guard so resize
  without actual SIGWINCH doesn't blank the terminal (terminal-ui.js)
- Sync _lastResizeDims on explicit resize to prevent redundant clears

CJK input rewrite (input-cjk.js):
- Use InputEvent.inputType to distinguish insertText (final) from
  insertCompositionText (tentative) — fixes Chinese punctuation and
  English text being swallowed during Android IME composition
- Remove isComposing guard on Enter so it always sends
- Phantom character (U+200B) keeps textarea non-empty so Android
  long-press backspace generates continuous deleteContentBackward
  events at the keyboard's native repeat rate

CJK input settings:
- Add "CJK Input" toggle in Settings > Input (index.html, settings-ui.js)
- Store as device-specific setting (cjkInputEnabled), not synced to server
- Replace INPUT_CJK_FORM env var dependency with user-controlled setting
  (env var still works as server override)

Mobile layout:
- Fix welcome screen overflow on phones by constraining .welcome-content
  to calc(100vw - 1.5rem) (mobile.css)
- Move xterm helper textarea on-screen for touch devices to fix iOS
  keyboard input (styles.css)
- Focus terminal synchronously in user-gesture context for iOS Safari
  keyboard activation (session-ui.js, app.js)
- Refocus terminal on tap (not scroll) in touch handler (terminal-ui.js)

src/web/public/terminal-ui.js

@@ -174,12 +174,14 @@ Object.assign(CodemanApp.prototype, {
       // Accumulate sub-line pixel deltas so slow swipes still scroll
       let pixelAccum = 0;
 
+      let didScroll = false; // track whether touchmove fired (tap vs scroll)
       container.addEventListener('touchstart', (ev) => {
         if (ev.touches.length === 1) {
           touchLastY = ev.touches[0].clientY;
           velocity = 0;
           pixelAccum = 0;
           isTouching = true;
+          didScroll = false;
           lastTime = 0;
           if (scrollFrame) { cancelAnimationFrame(scrollFrame); scrollFrame = null; }
         }
@@ -187,6 +189,7 @@ Object.assign(CodemanApp.prototype, {
 
       container.addEventListener('touchmove', (ev) => {
         if (ev.touches.length === 1 && isTouching) {
+          didScroll = true;
           const touchY = ev.touches[0].clientY;
           const delta = touchLastY - touchY; // positive = scroll down
           pixelAccum += delta;
@@ -207,6 +210,12 @@ Object.assign(CodemanApp.prototype, {
         if (!scrollFrame && Math.abs(velocity) > 0.3) {
           scrollFrame = requestAnimationFrame(scrollLoop);
         }
+        // Tap (no scroll): refocus xterm's hidden textarea so keyboard input
+        // routes back to the terminal. Without this, a tap on the terminal area
+        // consumes the touch event but xterm's textarea never regains focus.
+        if (!didScroll && this.terminal) {
+          this.terminal.focus();
+        }
       }, { passive: true });
 
       container.addEventListener('touchcancel', () => {
@@ -260,17 +269,6 @@ Object.assign(CodemanApp.prototype, {
           }
           this.flushFlickerBuffer();
         }
-        // Clear viewport + scrollback for Ink-based sessions before sending SIGWINCH.
-        // fitAddon.fit() reflows content: lines at old width may wrap to more rows,
-        // pushing overflow into scrollback. Ink's cursor-up count is based on the
-        // pre-reflow line count, so ghost renders accumulate in scrollback.
-        // Fix: \x1b[3J (Erase Saved Lines) clears scrollback reflow debris,
-        // then \x1b[H\x1b[2J clears the viewport for a clean Ink redraw.
-        const activeResizeSession = this.activeSessionId ? this.sessions.get(this.activeSessionId) : null;
-        if (activeResizeSession && activeResizeSession.mode !== 'shell' && !activeResizeSession._ended
-            && this.terminal && this.isTerminalAtBottom()) {
-          this.terminal.write('\x1b[3J\x1b[H\x1b[2J');
-        }
         // Skip server resize while mobile keyboard is visible — sending SIGWINCH
         // causes Ink to re-render at the new row count, garbling terminal output.
         // Local fit() still runs so xterm knows the viewport size for scrolling.
@@ -284,6 +282,19 @@ Object.assign(CodemanApp.prototype, {
           if (!this._lastResizeDims ||
               cols !== this._lastResizeDims.cols ||
               rows !== this._lastResizeDims.rows) {
+            // Clear viewport + scrollback ONLY when dimensions actually change.
+            // fitAddon.fit() reflows content: lines at old width may wrap to more rows,
+            // pushing overflow into scrollback. Ink's cursor-up count is based on the
+            // pre-reflow line count, so ghost renders accumulate in scrollback.
+            // Fix: \x1b[3J (Erase Saved Lines) clears scrollback reflow debris,
+            // then \x1b[H\x1b[2J clears the viewport for a clean Ink redraw.
+            // IMPORTANT: Only clear when we're actually sending SIGWINCH (dims changed).
+            // Clearing without a subsequent Ink redraw leaves the terminal blank.
+            const activeResizeSession = this.activeSessionId ? this.sessions.get(this.activeSessionId) : null;
+            if (activeResizeSession && activeResizeSession.mode !== 'shell' && !activeResizeSession._ended
+                && this.terminal && this.isTerminalAtBottom()) {
+              this.terminal.write('\x1b[3J\x1b[H\x1b[2J');
+            }
             this._lastResizeDims = { cols, rows };
             fetch(`/api/sessions/${this.activeSessionId}/resize`, {
               method: 'POST',
@@ -1261,6 +1272,10 @@ Object.assign(CodemanApp.prototype, {
     if (this.fitAddon) this.fitAddon.fit();
     const dims = this.getTerminalDimensions();
     if (!dims) return;
+    // Update _lastResizeDims so the throttledResize handler won't redundantly
+    // clear the terminal for the same dimensions (which would blank the screen
+    // without a subsequent Ink redraw to repaint it).
+    this._lastResizeDims = { cols: dims.cols, rows: dims.rows };
     // Fast path: WebSocket resize
     if (this._wsReady && this._wsSessionId === sessionId) {
       try {