feat: improve session resume reliability and persist user settings

- Filter empty sessions from history API (check for conversation content)
- Add --resume fallback to new session if resume fails (prevents dead panes)
- Pass resumeSessionId through respawnPane for dead pane recovery
- Persist respawn presets and runMode to server settings (cross-device sync)
- Fix mobile touch handling for Recent Sessions dropdown (DOM API + touch CSS)

src/web/public/index.html

@@ -330,6 +330,9 @@
               <button class="run-mode-option" data-mode="opencode" onclick="app.setRunMode('opencode')">
                 <span class="run-mode-dot opencode"></span>OpenCode
               </button>
+              <div class="run-mode-sep"></div>
+              <div class="run-mode-header">Recent Sessions</div>
+              <div class="run-mode-history" id="runModeHistory"></div>
             </div>
           </div>
           <div class="tab-count-group" title="Instance count">